Shortly after Pavlov’s investigations of the main digestive glands established his international reputation as a physiologist, his initially perfunctory attention to the relatively minor salivary glands precipitated a dramatic change in direction and launched the research that would make him an icon of twentieth-century science and culture. The psyche, formerly the somewhat capricious ghost in the digestive machine and a flexible variable for interpreting experimental results, became itself Pavlov’s explanatory target. “Psychic secretion” became also “conditional reflex”—and Pavlov launched a grand three-decade scientific quest to use this simultaneously physiological and psychological phenomenon to understand the psyche in deterministic, physiological terms.
The lab had devoted little attention to the salivary glands in the 1890s, but this research moved easily along the standard investigatory sequence. In 1893, Pavlov assigned coworker Sergei Ostrogorskii to confirm nervous control over the glands. A former coworker, David Glinskii, working independently, accomplished the next step: development of an improved fistula that allowed the separate collection of fluids from the three salivary glands (the parotid and the two mucous glands, the submaxillary and sublingual). Glinskii confirmed Bernard’s earlier observation that the various salivary glands responded differently to the same exciter and that they were “extraordinarily sensitive to the dryness of food.” Pavlov relied on Glinskii’s results in his report of 1895 to the Society of Russian Physicians that the work of the salivary glands, like that of the pancreatic and gastric glands, was “entirely purposive and individualized.”1
The few pages devoted to the salivary glands in Lectures affirmed that, like the main glands, they were controlled by nerves, responded only to specific exciters, and secreted purposively. Saliva was the first fluid to greet food on its entrance into the digestive factory and “must, therefore, provide a good welcome to the entering substances.” If food was dry, a watery saliva moistened it; if it was hard and bulky, a mucous secretion facilitated its passage down the narrow esophagus. Saliva also initiated the chemical processing of some foods (such as starch) and served as a “washing-out fluid” when injurious substances entered the mouth.2
The salivary glands responded even more markedly to psychic excitation than did the main glands. This had long been known to various investigators, and Pavlov presented it as a familiar observation: “Daily experience has shown us that the salivary glands become active even before food reaches the mouth. With an empty stomach, the sight of food or even the thought of it suffices for the salivary glands to immediately set to work, which is the basis of the well-known expression that ‘one’s mouth is watering.’ Therefore, a psychic event, the passionate longing for food, is undoubtedly an irritant of the nervous centers of the salivary glands.”3
The next step in Pavlov’s standard investigative sequence was to determine the specific excitants of salivation and the pravil’nost of salivary work. He entrusted this task to Sigizmund Vul’fson, who fulfilled the chief’s wishes with skill and dispatch. From March 1897 through February 1898, he experimented with four dogs equipped with fistulas of the different salivary glands, analyzing the quantity and quality of glandular reactions to teasing and feeding with various edible and inedible substances. He reported on his results to the Society of Russian Physicians twice and in 1898 completed his thesis, The Work of the Salivary Glands.
Vul’fson identified a “strict purposiveness” in the work of the glands. The salivary response to edible substances varied in quantity according to the dryness of the food and was uniformly rich in mucin (mucus). Inedible substances elicited “about the same” quantity as did foods, but the mucin level was generally low and varied little from one inedible substance to another. This, Vul’fson observed, made good sense. Mucin served to lubricate a foodstuff for its passage down the digestive canal. Since the dog did not swallow inedible substances, but rather ejected them from its mouth, a watery saliva low in mucin was secreted to rinse out any remnants of the ejected substance that remained.4
Vul’fson also discovered something unexpected and unique about psychic secretion in the salivary glands: it was a “complete reflection of the direct, purely physiological secretion, differing only in amount.” The glands produced the very same watery secretion when a dog was teased with dry food as they did when the animal actually chewed the food, the very same low-mucin secretion when teased with an inedible substance as when that substance was actually in the mouth, and, even if the dog was very thirsty, no saliva at all when teased with water, just as none was secreted when water was actually ingested. Psychic secretion in the salivary glands, then, differed in one important way from that in the main digestive glands: it was identical in composition to secretion during the second, nervous-chemical phase of digestion. It manifested the same ability to differentiate subtly among substances that, in the gastric and pancreatic glands, occurred only in the nervous-chemical phase of digestion, when, according to lab doctrine, the specific excitability of nerve endings generated the various characteristic secretory curves for different foods.5
Thus, the specific and purposive responses of the salivary glands, Vul’fson noted, involved not only “emotion, but also an element of thought—a representation about the nature of the external substances” the animal was ingesting. The adaptation of salivary reactions to specific substances was “almost entirely of a psychic nature.” The psyche’s task was “to sort out” objects into various groups in order to respond to each appropriately, a task in which it exhibited great “scrupulousness,” an “unerring judgment of particular circumstances,” and the ability to “generalize.”6
Two experiments were especially telling. One concerned the salivary response to a combination of meat and mustard oil. When the dog ate meat alone, a mucin-rich saliva facilitated the meat’s passage down the esophagus; when it was fed mustard oil (a most unpleasant substance), the glands produced a watery saliva to wash out the mouth. When mustard oil was added to meat, the result was not a simple summing of these responses, but rather a watery saliva appropriate to a rejected substance. The psyche, then, had transcended mere chemical responses to render a judgment, to categorize the combination as a rejected substance. Similarly, rocks and sand of identical chemical composition produced different results when introduced into a dog’s mouth. The former elicited no salivation (since the dog simply spit it out), and the latter a great deal of mucin-rich fluid (as the dog must wash down its throat the small grains that invariably remained after attempting to spit out the sand). Psychic secretion produced precisely the same two results, distinguishing purposively between rocks and sand. Clearly, Vul’fson informed the Society of Russian Physicians in March 1898, the psyche was making an acute judgment here, and further investigation “must move to the psychology of salivation.”7
A delighted Pavlov lauded Vul’fson’s report (which, of course, he had closely edited) for demonstrating the “subtle and sharp adaptation of the salivary glands,” and emphasized that in salivation “the participation of the psyche emerges clearly, so psychology almost entirely overshadows physiology.” This “dominance of psychology” was especially clear from “the fact that appropriate types of saliva are secreted both when a tested substance is put into the mouth and when it is only used to tease the dog.” Here, clearly, the investigator confronted “the mind of the glands.”8
The specific qualities of this “mind” presented an obstacle to Pavlov’s standardized investigative path. For years, he and his coworkers had recognized the importance of the psyche but had black-boxed it. When analyzing gastric secretion, for example, they simply attributed a dog’s initial secretory reaction to foodstuffs to “the psyche” in the form of appetite. There had been no need to explore the nature and mechanism of that psychic response, especially as it gave way in the second phase of the digestive process to the specific nervous mechanisms that produced the all-important characteristic secretory curves. Vul’fson’s experiments, however, demonstrated the inapplicability of this schema to the salivary glands by demonstrating that here the psychic secretion was essentially identical to the nervous-chemical secretion, differing only in amount. The purposive, precise, and specific reactions of these glands to different foods resulted, then, not from the specific excitability of the nervous system (as was presumably the case for the gastric and pancreatic glands) but rather from the psyche’s ability to, as Vul’fson put it, “sort out,” “arrange,” and “judge.” The Pavlovian program for digestive physiology now seemed to lead directly into the psychology of the salivary glands.
Recognizing that here “psychology almost entirely overshadows physiology” and conceding his own lack of expertise in this area, Pavlov abandoned a longstanding managerial practice and turned to an outside expert. His new collaborator, Anton Snarskii, was a most atypical coworker. A physician who had served in the military and the struggle against Russia’s disastrous cholera epidemic of 1892–1893, he had worked in neurologist-psychiatrist Vladimir Bekhterev’s clinic for mental and nervous illnesses before becoming a clinician at the Alexander III Charity Home for the Mentally Ill, near St. Petersburg, where Pavlov’s friend Alexander Timofeev was director. Throughout the 1890s, Pavlov had been visiting that facility frequently on Sundays, joining Timofeev for sessions with especially interesting patients and discussions with the psychiatrist’s wide circle of friends. It was probably during one of these visits that Pavlov met Snarskii and recognized in him an appropriate partner for exploration of the psychology of salivation. The two conceived a mutually beneficial arrangement: Snarskii would lend his expertise to investigations of the “mind of the glands” and in the process would earn a quick doctorate. Unlike the typical coworker, then, Snarskii entered the lab to study a particular subject in which he possessed greater expertise than the chief.
This atypical coworker produced a most atypical dissertation. Unlike the vast majority of his predecessors, he drew extensively upon scientific authorities outside the lab, citing physiologists who had addressed the biology of purposive behavior (including Jacques Loeb and Ivan Sechenov) and a number of Russian and Western psychologists (including Georgii Chelpanov, William James, and Wilhelm Wundt).
Snarskii invoked these authorities to criticize Vul’fson’s (and Pavlov’s) conclusion that, in salivary secretion, the psyche actively chose, arranged, and judged. By the standards of contemporary psychology, he insisted, Pavlov’s “mind of the glands” did not deserve the word “mind.” Like the psychologists whom he cited, Snarskii distinguished among a wide variety of mental qualities that involved a broad range of different capacities. He concluded that psychic secretion reflected not high-level processes such as will, choice, and judgment, but rather the relatively low-level process of “visual associations.” Psychic secretion resulted from “the simplest process that united new impressions with preceding ones: elementary memory.” As the simple result of associations, such memory was devoid of the higher-level psychological qualities that Vul’fson and Pavlov had attributed to it.9
Psychic secretion, then, was but an association or “habitual reflex”; choice had nothing to do with it:
When the dog recognizes a previous irritant...it repeats a habitual reflex; but repeats it automatically, without any participation of conscious, active will. Schematically, this would be expressed as follows: a common reflexive arc is established between the direct irritant and the act of salivation.... This act is accomplished entirely stereotypically, automatically, via a well-trod path. The consciousness of the dog plays no “important” role; it “chooses” nothing and in itself does not “determine” the activity of the salivary glands.10
Here Snarskii used one of Pavlov’s favorite words, stereotypical, to make his point. This was a determined, physiological process characterized by “stability, consistency, automaticity, and the absence of the novelty and indecisiveness that appear together with consciousness.”11 Snarskii, then, reinterpreted as simple associations experimental results that Vul’fson and Pavlov had attributed to the psyche’s choices. For example, when a substance, such as acid, that elicited a salivary reaction was tinted black and poured into a dog’s mouth, “there is apparently established a visual association between the caustic taste and the substance’s color; correspondingly, a reflex is established.” Therefore, black-tinted water elicited the same response. If that water was then poured repeatedly into the dog’s mouth, however, the salivary response ceased, since it did not irritate the roof of the dog’s mouth. If black-tinted acid was again poured into the dog’s mouth and the experimenter then feigned putting black-tinted water into the dog’s mouth, salivation again occurred. “It is clear that the dog, on the basis of the just-established reflex, repeats the very same reflex, defending the mucus [mucous membrane] of the mouth from the corrosive action of the acid. Two signs—acid and color—turn out to be linked, and the dog reacts identically to one and the other without judging and without choosing.”12
The “psychic moment” in salivation, then, was most definitely not, as Vul’fson (and Pavlov) had concluded, “liberated from the guardianship of physiology.” Rather, “I think that the psychic element is a later superstructure, established through experience, and is therefore not independent but subordinate.” (Snarskii used first-person language here, which was unusual for the lab’s theses and perhaps reflected a disagreement with the chief.) This psychic superstructure facilitated the adaptation of organisms to their environment and existed even among relatively simple organisms, as Loeb had demonstrated for the invertebrate sea squirt.13
Snarskii was drawing upon contemporary psychology to challenge the lay, black-boxed notion of the psyche that had governed lab interpretations throughout the 1890s. His approach to psychic secretion was both truer to contemporary trends in psychology and “more physiological” than that previously propounded by Vul’fson and Pavlov.
Yet Snarskii’s thesis did not offer a clear path forward. Pavlov knew little about psychology and was uncomfortable with the procedures, terminology, and philosophical problems associated with that discipline. Even if he accepted Snarskii’s basic conclusions, he lacked any methodology to address psychic secretion (or associations or complex reflexes) in a manner consistent with his notion of good physiology and his own strengths as a researcher. So he again searched outside his lab for, as he later put it, “a person with whom one could go further.”
He chose a second atypical coworker, Ivan Tolochinov. Like Snarskii, Tolochinov was a veteran of Bekhterev’s lab and a clinician at Timofeev’s Charity Home. Unlike Snarskii, he had already earned his doctoral degree—so he enjoyed an unusual relationship of virtual equality with the chief. He did not require Pavlov’s approval, and they worked together not as chief and coworker but as colleagues. “He was already a doctor and worked with me purely from scientific interest,” Pavlov later recalled. “Ivan Filippovich became very close to my heart, became a person very close to me.”14
Their relationship ended badly, and they later provided very different accounts of their collaboration, but these agree on three main points. Tolochinov conducted most of the experiments, sometimes with Pavlov’s participation. Tolochinov was largely responsible for the initial experimental and conceptual breakthroughs; as Pavlov observed, “he was the first to put his hand to it; priority, one could say, belonged to him.” And Pavlov fundamentally reinterpreted Tolochinov’s findings—as reflected in his replacement of Tolochinov’s term for psychic secretion, reflex at a distance, with his own term, conditional reflex—and conceived an experimental line of inquiry to build upon Tolochinov’s initial results.
From November 1901 through early June 1902, Tolochinov traveled from the Charity Home to Pavlov’s lab several afternoons a week to conduct experiments for about three hours at a time. Like Pavlov, he initially described psychic secretion according to the post-Snarskii lexicon, using such psychological terms as “representation” and “association.” Babkin later recalled that, in order to avoid “extrinsic influences,” the taciturn Tolochinov conducted experiments in a separate room where Pavlov stopped by periodically.
[Tolochinov] was an extremely quiet and withered man. It is impossible to remember without smiling the manner in which he carried out his experiments. He slowly waved a rusk in the dog’s face a certain number of times. The dog licked its chops and saliva dripped from the fistula which had been made in one of its salivary glands for the purposes of these experiments. This was a conditional reflex. Then Tolochinov invariably tapped the dog gently on the head with the rusk, after which the animal was allowed to eat it—this was an unconditional reflex. This ritual never varied and was always conducted in the same methodical and melancholy fashion.15
Tolochinov’s main task was to acquire consistent results, to establish that psychic secretion was lawful and regular (pravil’nyi). He waved various substances in the dog’s face: toast, fingers smeared with meat powder, open bottles of mustard oil and hydrochloric acid. He tested the effect of stimulating various sensory organs—for example, with both the sight and scent of meat powder or mustard oil—and varied the distances and time intervals at which he did so. He soon discovered that psychic secretion depended upon the dog being very hungry, and that, as the lab had discovered years ago, it was much more easily elicited in some dogs than in others.
In early February 1902, working with a female dog, Ryzhaia, who had proven especially prone to psychic secretion, Tolochinov made the key breakthrough from which Pavlov would always date the true beginning of research on conditional reflexes: the discovery of what would later be termed “extinction.” Waving dry toast in a hungry Ryzhaia’s face would first produce, say, 0.2 cubic centimeters of secretion; repeating this same procedure three minutes later elicited only 0.1 ccs., and repeating it yet again produced no secretion. The same pattern of regular decline until “extinction” held also when Ryzhaia was exposed to the sound of scraping a piece of hidden toast on a plate, the scent of hidden moist meat powder, and other stimuli. This, Tolochinov later recalled, imparted “a new direction both to my work and to that of subsequent investigators in this sphere.”16
Tolochinov’s attention to and pivotal interpretation of this result drew upon his experience in psychiatry with the knee and eyelid reflexes. Since psychic secretion behaved similarly to those well-known reflexes, there was no need to resort to psychological terms in order to analyze them:
It had been noticed long ago that in several patients knee reflexes sometimes result, not only from the blow of a hammer, but even when this instrument is merely waved with the intention to strike the [knee].... It is also remarkable that this phenomenon is to a certain degree involuntary; therefore it is most easily understood as a reflexive act from the brain cortex by means of waves of light, just as the reflexive response of the knee to a blow is the result of mechanical waves. This is the same type of phenomenon as the nictitating reflex of the eyelid, which occurs not only when the eyelid is touched, but also when any object, or the investigator’s fingers, make a more or less rapid approach to the eye.
On these foundations I proposed that the phenomenon of salivation during irritation of the dogs at a distance by foodstuffs be considered a reflex at a distance, which was accepted by Prof. I. P. Pavlov, who termed it a conditional reflex, as distinct from the unconditional reflex received when the mucous membrane of the roof of the mouth is irritated directly by edible and inedible substances.17
Psychic secretion, then, behaved precisely as did the nictitating reflex of the eyelid and the knee reflex. Tolochinov had learned in Bekhterev’s clinic, where these reflexes were studied intensively and used to diagnose nervous and mental diseases, that, like psychic secretion, the eyelid and knee reflexes were elicited without direct physical contact, yet behaved in a regular, lawful fashion—as was most dramatically evident in the “law of extinction.”18
Just as Snarskii had drawn upon authorities in psychology to strip the “mind of the glands” of will and judgment—to portray psychic secretion as a simple “association or habitual reflex”—so did Tolochinov draw upon clinical psychiatry to establish that psychic secretion behaved similarly to other “reflexes from a distance” that were “distinguished by an involuntary, fatal character.” For Pavlov, this rendered it, at least in principle, accessible to physiological investigation.
The phenomenon of extinction also provided some firm ground on which to stand and observe other regularities governing this complex reflex. From mid-February through early June 1902, Tolochinov and Pavlov used extinction as a background phenomenon for identifying increasingly complex regularities. They discovered, for example, that an extinguished conditional reflex could be rekindled by exciting the unconditional reflex on which it depended. They explored the secretory effects of alternating various stimuli, of burning the dogs with hot wires on parts of their body (some within reach of the dog’s mouth and so eliciting protective salivation, some out of reach), of feeding one dog in the presence of another (this lessened psychic secretion), and of denying the dog food for up to six days (the same regularities obtained, but in sharper form).19
In July 1902, Tolochinov joined a delegation of Pavlov’s coworkers that delivered reports to the Northern Congress of Physiologists in Helsingfors (Helsinki). Speaking in French, he unveiled Pavlov’s term conditional reflex (réflexe conditionnel), explained how one obtained such a reflex in a lab dog, and briefly discussed the phenomenon of extinction. Reporting his discovery that a number of simple salivary reflexes originated with the trigeminal nerve that ran from the mucous membrane of the nose, he explained: “This is why we oppose to the immediate and absolute reflexes—that is, to the reflexes of the mucus [mucous membrane] of the nose and mouth cavities—all the other effects on the salivary glands that are ordinarily determined to be psychic effects and which we term conditional reflexes.” To obtain a conditional reflex, the animal must be “more or less starving,” and “one must take advantage of an immediate reflex.” That reflex “weakens little by little and disappears if, having first allowed the dog to eat, one excites him again by showing the same food.” Conditional reflexes could be obtained by exciting various sensory organs with food or inedible substances by sight, sound, or smell, and the greatest secretory effect was obtained by exciting an ensemble of sensory organs simultaneously. Finally, Tolochinov noted that the conditional reflex responded sensitively to complex properties; for example, despite a “great desire” for meat powder, the dog did not salivate on being shown meat powder moistened with water (since ingestion of this moist substance did not require salivation).20
Tolochinov’s research, however, was about to end. He soon became estranged from Pavlov, returned to clinical practice in the Charity Home, and for years failed to write up the bulk of his experimental findings for publication. Finally, in 1912–1913—by which time Pavlov had been working on the subject for some eight years—he infuriated his former collaborator with a series of articles in which he published the protocols of his experiments, claimed a large share of the credit for the birth of conditional reflex research, and criticized the direction that research had taken in subsequent years. In his own accounts of their collaboration, Pavlov always acknowledged Tolochinov’s fundamental contribution, but cast his failure to write up his research promptly as an example of “the undisciplined Russian character” and his later articles as a pathetic mixture of “fact and fantasy” and a personal betrayal.21
However intriguing and significant, Tolochinov’s research did not in itself convince Pavlov to shift investigations from digestion to the psyche. The lab, after all, was constantly uncovering new phenomena and research possibilities, many of which were never pursued. As both an experimental physiologist and the manager of a large laboratory enterprise, Pavlov evaluated this possible new line of research by both scientific and managerial criteria. As a scientist, he asked whether investigations of the psyche, like research on digestion, could generate precise, repeatable, purposive patterns that could be expressed quantitatively. As a manager, he wanted to know whether the subject could consistently generate fresh dissertation topics that could be satisfactorily completed by physiologically untrained physicians within two years.
As Pavlov pondered these questions from 1901 to 1904, he was also influenced by other considerations. First, the very nature of digestive physiology was changing, making it considerably less attractive. The discovery of secretin by Bayliss and Starling in 1902 had undermined his nervist portrayal of digestive processes, introducing, as one coworker put it, a certain “dissonance” in the lab. As a theorist, Pavlov could accommodate himself, however reluctantly, to the existence of humoral mechanisms; but as an experimentalist he found this more difficult. Furthermore, he simply found nervous mechanisms more aesthetically pleasing and, throughout the 1890s, had consistently avoided topics that forced him to confront humoral ones. New discoveries on the biochemistry and interaction of digestive ferments were also complicating Pavlov’s portrayal of digestive processes and moving discussions away from his strengths—away from organ physiology—into areas in which he neither enjoyed technical supremacy nor spoke with special authority.22
A second important factor was developments in Russian psychology and psychiatry that had normalized the previously controversial view that psychological phenomena might be explicable physiologically. Russian society had changed markedly since Pavlov’s youth, when biological approaches to mind seemed inextricably related to pressing ideological and political debates about the legitimacy of church and tsar. This connection seemed much more distant amid the great economic and social issues of the post-Reform era, when Russian intellectuals were preoccupied with socioeconomic conditions and political-economic theory rather than the relationship between mind and body.
In this context, biological approaches to mind had become increasingly the province of professionals with much narrower concerns. Physiologists, physicians, and psychiatrists of varying ideological and political stripe—men such as Vladimir Bekhterev, Sergei Korsakov, Pavel Kovalevskii, and a now more philosophically restrained Ivan Sechenov—developed biological and experimental approaches to mind with an eye to medical issues and practices. For most, the broader philosophical and political issues associated with biological psychology in the 1860s faded far into the background or were banished altogether from the province of positive science. Debates about materialism and idealism gave way (as Bernard had advocated) to methodological “realism,” to the study of proximate causes without speculation about ultimate ones. It was now widely accepted that a scientist could take a biological approach to mind without speculating about the existence or nature of spirit and the soul.
By the turn of the century, then, it was neither uncommon nor controversial to assert that what Pavlov termed psychic secretion might be a reflex. Pavlov found himself taking a considerably “less physiological” position toward psychic secretion than did a number of his medical students, who, as coworker Lev Orbeli recalled, “often asked: but can’t this be explained as a reflex, just one from another sensory organ?” Snarskii and Tolochinov had themselves worked in Bekhterev’s lab at the Military-Medical Academy, where, in their studies of brain localization, the neurologist-psychiatrist and his coworkers approached psychic secretion as “nothing other than a reflex.”23
Finally, Pavlov had long been interested in the mysteries of the human mind (and in psychiatry) and had imbibed in the 1860s a positivist faith that a scientific understanding of the psyche was the surest path to the rational control of human destiny, to social progress. He later recalled of his decision to study conditional reflexes that “the most important impetus for my decision, although at the time an unconscious one, was the influence, from the long distant years of my youth” of Sechenov’s Reflexes of the Brain. This invocation of Sechenov must be taken with a grain of salt—and it was the psychologist Snarskii, and not Pavlov, who first invoked Sechenov in lab publications. Yet this new research possibility may well have appealed to Pavlov as a way of using the disciplined methodology of the mature scientist to explore a former passion of his “youthful mind” and to pursue the longstanding interest in human psychology that he had also expressed in his correspondence with Serafima about Dostoevsky in 1880, but had pronounced beyond the competence of current science.24
Research on the psyche represented a risky leap into uncharted territory, and his decision-making process proved slow and contradictory. As one longtime coworker later recalled, he “suffered through a great series of doubts and vacillations.” In July 1902, after Tolochinov delivered his paper in Helsingfors, another coworker watched Pavlov speak animatedly to scientists in the corridor about the potential of this new line of investigation and his plans to pursue it. “He was in a state of great agitation.... ‘Yes, we’ve got it, look what we’ve got!’ And he added: ‘You know, there is enough work here for many decades.’ A few months later he was proclaiming to new coworkers: “Down with the physiology of digestion. And you all...I will turn to the study of the nervous system.”25
Yet the response of Pavlov’s colleagues in the Helsingfors corridor was unenthusiastic, and in his lectures on digestive physiology a few months later he discussed psychic secretion precisely as he had before Tolochinov’s (and even Snarskii’s) experiments: the dog “can think, desire and express its feelings. It follows instructions, guesses, shows what is pleasant and unpleasant for it.” If one dyed acid black, poured it into the dog’s mouth, and then pretended to be about to do so again, “the dog guesses that this is an unpleasant substance; it knows this from preceding experiments, and salivation begins.”26
There was no crucial experiment, no eureka moment during which Pavlov became convinced that psychic secretion could be productively approached as a reflex. Yet we can track his transition. In comments of February 1903 to the Society of Russian Physicians, he offered a somewhat embarrassing recantation of his longstanding denial of purely mechanical exciters of the salivary glands. This shift in position was necessary to conceptualizing those mechanical exciters as the basis of an unconditional reflex, which he would oppose to the conditional reflex of psychic secretion.27 Two months later, Pavlov delivered his first public address on conditional reflexes to the International Medical Congress in Madrid. In 1903, he assigned only one of five new coworkers to the new line of investigation, but, significantly, in October 1903 he pulled a favorite collaborator, Babkin, off an important investigation of the pancreas to work instead on conditional reflexes. In 1904, most of Pavlov’s coworkers left for the front in the Russo-Japanese War, yet he assigned one of his two new coworkers, Nikolai Tikhomirov, to the new line of investigation and devoted much of his high-profile Nobel Prize speech to this research. In 1905 he assigned two of three, in 1906 three of four, and in 1907 all new coworkers to the new research. In his annual reports to Prince Ol’denburgskii, Pavlov first mentioned the new line of investigation in his report of December 1903. He listed it last among the lab’s research topics from 1903 to 1906, and as the only topic in 1907.28
What exactly, for Pavlov, was a conditional reflex? Why did he use this term, uslovnyi refleks, to replace Snarskii’s association or habitual reflex and Tolochinov’s reflex at a distance?
For Tolochinov, the term reflex at a distance captured what he considered essential about this phenomenon: it was a determined, reflexive response elicited, like those from the knee and the eyelid, without physical contact. Like some of Tolochinov’s experiments, this term also suggests he was thinking in terms of an analogy from Newtonian physics, in which (Newton’s reservations notwithstanding) gravity was “action at a distance.”29 According to Orbeli, who worked from 1901 to 1917, Pavlov used the term conditional reflex “in part because their very inclusion as reflexes then had for him a conditional character.” This fits Pavlov’s common use of the word uslovnyi, “conditional,” as a synonym for “tentative” or “hypothetical.”30
For Pavlov, the term conditional reflex reflected not only whatever ontological reservations he may initially have had, but also, much more importantly, the test this potential new line of investigation had to pass in order to qualify as good physiology. By its very nature, the conditional reflex was dependent upon particular conditions. Unlike the unconditional reflex, it existed under some conditions and vanished under others. The conditional reflex offered a legitimate subject for Pavlov only if these conditions themselves, the dependence of the conditional reflex upon them, and the dynamics of that reflex were fully determined.
In his first public statement on this new research in 1903, Pavlov rejected Tolochinov’s notion that the difference between simple physiological reflexes and psychic secretion was that the former resulted from the organism’s direct contact with an exciter and the latter from action at a distance. In “psychic experiments,” Pavlov reasoned, an object stimulated the animal’s salivary glands by acting on various bodily surfaces—the nose, eyes, or ears—“by means of the environment (the air, the ether) in which both the organism and the irritating substance are located.” This was a form of direct contact and resembled many “simple physiological reflexes” that were transmitted through the same organs.31
The essential difference between unconditional and conditional reflexes, then, resided elsewhere. In the former, “physiological case, the activity of the salivary glands is linked with the same qualities of the object upon which the effect of the saliva is directed.” These qualities excited the specific nerve endings in the roof of the mouth. Therefore, “in physiological experiments the animal is irritated by the essential, unconditional qualities of the subject, by those related to the physiological role of saliva.” This was an unconditional reflex. In psychic experiments, on the other hand, the animal is irritated by “the qualities of external objects that are inessential or even completely accidental in relation to the work of the salivary glands.” For example, the visual and olfactory properties of meat could elicit psychic secretion although these had no “business relation” to the work of the glands. Indeed, in psychic experiments the salivary glands could be stimulated by “absolutely everything in the surroundings,” including the dish in which the substance was presented, the attendant who bore it into the room, the noises he made, and so forth. “So in psychic experiments the connection of objects irritating the salivary glands becomes altogether distant and subtle.” This was the conditional reflex.32
Both the promise and the peril of research on psychic secretion resided in this conditionality of the relationship between stimulus and response.33 On the one hand—and this was Pavlov’s gut feeling—this conditionality perhaps represented the animal’s complex but determined adaptation to the subtlest change in its conditions—to changing signals about available food or an approaching predator. By means of “the distant and even accidental characteristics of objects, the animal seeks food, avoids enemies, and so forth.” On the other hand, this conditionality might represent the indeterminacy of the idiosyncratic psyche or a determinacy inaccessible to physiological methods. In that case, conditionality would deprive experiments on this subject of the determinedness, the pravil’nost’, that was the sine qua non of good physiology.
As Pavlov put this central question in 1903 (answering it, perhaps, with a bit more conviction than he actually felt):
The center of gravity in our subject lies, then, in this: is it possible to include all this apparent chaos of relations within certain bounds, to make these phenomena constant, to discover their rules and mechanisms? It seems to me that the several examples which I shall now present give me the right to respond to these questions with a categorical “yes” and to find at the basis of all psychic experiments always the very same special reflex as a fundamental and most common mechanism. True, our experiment in physiological form always gives one and the very same result [whereas]...the basic characteristic of the psychic experiment, on the other hand, is its inconstancy, its apparent capriciousness. Nevertheless, the result of the psychic experiment also recurs, otherwise we could not even speak about it. Consequently, the entire matter resides only in the great number of conditions influencing the result of the psychic experiment as compared with the physiological experiment. This will be, then, a conditional reflex.34
The conditional reflex, then, was a suitable subject for physiological research only if was actually fully determined. As an experimentalist and lab manager he defined this issue operationally: to what extent can pravil’nye results be acquired in the lab? This is what made Tolochinov’s discovery of extinction so important—it represented the first case in which a conditional reflex behaved in a quantifiably repeatable, orderly fashion. After Tolochinov’s report in Helsingfors, he, and then Babkin, conducted various experimental trials that reinforced Pavlov’s intuition that conditional reflexes were indeed governed by “firm lawfulness” and so experiments upon them could produce “constantly recurring facts.” This ability to generate consistent results was the consistent theme of his initial speeches on his new line of investigation. Psychic experiments were “lawful, since they can be repeated as often as one wishes, like ordinary physiological phenomena, and can be systematized in a definite manner.” In the lab’s first doctoral thesis on conditional reflexes, Babkin, too, emphasized “the constancy of phenomena [and] the ease with which they can be reproduced.”35 Once Pavlov became convinced that the conditional reflex was fully determined, the varying results of different experiments were attributed to uncontrolled variables, to still-undiscovered conditions governing the reflex.
Pavlov, then, addressed the conditional reflex in basically the same manner as he had digestive physiology. Feeding the same dog the same quantity of the same food in two different experiments had never, after all, yielded exactly the same secretory results. The differences were explained by reference to the dog’s personality, mood, and so forth, and his interpretation of the play of these variables was central to his attempt to identify meaningful patterns in the data (the characteristic secretory curves). Similarly, as we shall see, no two experiments on conditional reflexes produced precisely the same results—and the variations among dogs were especially striking. In this new research, however, the psyche no longer served as a flexible variable; it became, rather, itself the explanatory target. So Pavlov’s search for meaningful patterns in experimental data led him constantly to expand the field of his explorations and explanations in search of the innumerable factors in the animal’s constitution, history, and environment that influenced its psychic responses.
In this way, “psychic secretion” became the “conditional reflex,” but—and this resided at the very heart of Pavlov’s quest over the next three decades—it also remained psychic secretion. For Pavlov, psychic secretion and conditional reflex were but two different dimensions of the same phenomenon. He did not seek to replace one with the other, but rather, as he often put it, to “fuse” them—to integrate the physiological understanding of “conditional reflex” with the equivalent psychological notion of “association,” the dynamics of what he termed “higher nervous activity” with those of experimental psychology, the objective with the subjective.
His great excitement about this research flowed precisely from its possibilities for experimental psychology in the broadest and most ambitious sense of that term—for a scientific understanding of the subjective world of animals and humans. The entire history of psychic secretion in his lab had imbued it with this broader meaning as a reflection of a dog’s personality and food tastes; of its greediness, self-possession, passionateness, or impressionability; of its ability to think, desire, and express its feelings.
Undertaking his new research, then, Pavlov did not suddenly reject the existence or importance of the subjective world and such long-familiar psychological qualities. Quite the opposite: he adopted them as his explanatory targets. “The phenomena of the conditional reflex, if one gives them their psychological term, are precisely...associations.” So, the salivary conditional reflex was “the substratum of elementary, pure representation, of a thought in the subjective world.” For Pavlov, then, exploration of the dynamics of conditional reflexes offered a method for analyzing the underlying mechanisms of personality, learning, expectation, emotions, and all the other qualities that he had long associated with psychic secretion and that many psychologists attributed to associations.36 Over the next decades, he and his coworkers would pay even greater attention to the psychological qualities of their dogs than they had during research on digestion, and they would discover that—aside from differing in their food tastes, impressionability, and greed—dogs were heroic and cowardly, crafty and dull, diligent and lazy, freedom-loving and passive, mentally robust and diseased. Such qualities, however, were no longer confined to a black box, for Pavlov believed that he had developed a scientific method for investigating them, for explaining them as the results of physiological processes.
Adopting the mantle of the objective physiologist and painfully aware of the difficulties of his quest, he would often muffle or cloak his goal in public presentations. Yet he proclaimed it quite clearly in his first speech on the subject in 1903: “Science will sooner or later bring the obtained objective results [of physiological experiments] to our subjective world, and will at once brightly illuminate our mysterious nature, will explain the mechanism and vital meaning of that which most occupies Man—our consciousness and its torments.”37