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Experiment as the Only Guide

Experiment as the Only Guide

Chapter:
(p.77) Chapter Five Experiment as the Only Guide
Source:
About Method
Author(s):
Jutta Schickore
Publisher:
University of Chicago Press
DOI:10.7208/chicago/9780226450049.003.0006

Abstract and Keywords

Felice Fontana’s Treatise on the Venom of the Viper; on the American Poisons; and on the Cherry Laurel, and some other Vegetable Poisons is considered a milestone in venom research. Throughout the nineteenth and early twentieth centuries, his research served as a starting point for investigations of snake venom, and his experimental methods were praised as exemplary. Fontana’s methods discourse was both as a creative appropriation of a long tradition and as a product of the challenges he encountered in his own endeavors. Fontana performed countless experiments to explore the effects of viper venom on the animal body, initially to confirm Redi’s (and Mead’s) view that the yellow liquor flowing from the viper’s protruding teeth was the substance that contained the poison. Like Redi and Mead, Fontana was a committed experimentalist. Unlike his predecessors, Fontana offered very detailed discussions of experimental strategies, emphasizing the significance of variations in experimental practice. The treatise describes numerous experiments on the nature and action of venom. As an integral part of the account, it offers detailed comments on proper procedure, describing countless variations and drawing attention to the circumstances of each trial.

Keywords:   snake venom, methods discourse, experimentation, variation, circumstances, Felice Fontana

Mead’s writings on poisons did not have any long-lasting effect on venom research. Felice Fontana’s substantial experimental project on viper venom, by contrast, was pivotal. In the eyes of toxicologists as well as of historians of science, Fontana’s work is a milestone. His Treatise on the Venom of the Viper; on the American Poisons; and on the Cherry Laurel, and some other Vegetable Poisons appears in almost all bibliographies related to venom research, both old and recent. Throughout the nineteenth and early twentieth centuries, his research served as a starting point for investigations of snake venom, and his experimental methods were praised as exemplary. Until the twentieth century, toxicologists cited his writings, and especially his methodological views, as a model for their own investigations. He was often characterized as innovator in matters methodological. As late as 1962, American herpetologist Laurence Klauber described Fontana as “the first of the great experimentalists to use adequate controls.”1 Fontana’s work is a treasure trove for the history of methods discourse, because he was very explicit about methodologies of experimentation. At the same time, his methodological ideas are not easy to interpret and situate—although he was an innovator for many, his writings also seem to bear striking resemblance to early modern texts. This chapter and the next will discuss the content and organization of Fontana’s methods discourse. Close reading is crucial; only if we pay attention to the exact arrangement of Fontana’s account can we assess whether and in what respects the methodology of experimentation he expounded really was innovative, unique, and pathbreaking, and how much he owed to tradition.

Like Redi, Fontana was naturalist to the Grand Duke of Tuscany (the reform-minded Pietro Leopoldo), and—also like Redi—he had ample (p.78) resources to pursue his investigations. Fontana was the director of the Florentine Museum of Natural History. In this capacity he traveled to major European cities, visited instrument makers, bought instruments for the collection, and conversed with the luminaries of his time. He was in charge of the famous collection of anatomical wax models housed by the natural history museum in Florence. His works, excerpted and reviewed in major scientific journals such as the Philosophical Transactions, were quickly translated into English.2

Fontana’s extensive treatise was published in two volumes in French in 1781, then in English translation six years later. It comprises a collection of texts on various topics—including the microscopic structure of nervous tissue and the regeneration of nerves—which were written at different times. According to the title, the treatise covered several poisons—viper venom, “American poisons” (especially curare or “Ticuna,” the arrow poison), and cherry laurel—but the book really is a treatise specifically on viper venom. Only a small portion of the text deals with those other substances.3

The organization of the work is rather confusing.4 There are two books (one from the 1760s, one from the 1780s) and two volumes, but part of the second book is included in volume I. The first volume contains a translation of Fontana’s early essay on experiments with snake venom, published in Italian in 1767. The Italian text refers to prior debates between Redi and his adversaries as well as to Mead. Considering that Mead’s Mechanical Account of Poisons did not contain much original research, its service as one of the main points of orientation for Fontana’s own investigations is worthy of note. In the introduction to the Italian text, Fontana acknowledged the achievements of both Redi and Mead and announced that he mainly wished to clear up some errors. These errors were not, as one might expect, theoretical errors but rather were incorrect experimental findings (although Fontana had something new to say about disease as well).

Fontana’s second (French-language) treatise on viper venom—the bulk of which is printed in volume I of the Treatise on the Venom of the Viper—is above all a response to Balthazar-Georges Sage’s publication on the chemical nature of viper venom and on volatile alkali as an antidote, a work that was at odds with Fontana’s view. Fontana’s book presents experiments made after the completion of the Italian treatise. These experiments refuted not only Sage’s position but also Fontana’s own previous findings, and Fontana took the occasion to comment at length on experimental practices and methods. The book even contains a methodological essay, (p.79) entitled “On the Source of Many Errours,” which deals with the problems and pitfalls of physiological experimentation.5 The second volume of the work concludes the discussion of the new experiments on vipers. It also contains the additional material dealing with the other poisons as well as microanatomical observations (including a discussion specifically on the problems of microscopical observation) and a supplement featuring descriptions of some more experiments and scattered comments on vipers and viper venom.6

How Theories Fall and Vanish before Experiment

Fontana’s Italian treatise on venom from 17677 confirmed Redi’s (and Mead’s) view that the yellow liquor flowing from the viper’s protruding teeth was the substance that contained the poison. The text begins with new observations of the teeth of the viper and the “vesicles” containing the venom, intending to clear up some anatomical facts that Redi had gotten wrong. The main part of the Italian treatise addresses the two issues that Mead had discussed—namely, the chemical nature of the yellow liquor and the mechanism of its working. Fontana showed that both Mead’s observations and experiments as well as his conclusions were wrong.

The series of editions of Mead’s Mechanical Account mirrored the development of eighteenth-century medical thought rather than the development of Mead’s own insights into the nature and working of poisons. The symptoms of snakebite were first explained as fermentations affecting the blood, then—when the focus of disease theory shifted from the blood to the nerves—as a nervous affliction. Fontana explained those symptoms in light of the latest development in medicine, the rise of Anatomia animata and its associated conceptions of irritability and sensibility.8 Not only did he discuss and refute Mead’s claim that viper venom was a salt, but he also advanced the view that the fluid affected the “irritable” tissues. Unlike Mead, however, he linked his theory to his own experimental findings.

Putting together the first edition of his Mechanical Account, Mead borrowed extensively from other scholars’ writings. Fontana, too, was inspired by other people’s ideas—theoretical as well as methodological—but he forged his own approach. Fontana’s new explanation of the working of viper venom is framed by a passage drawn from Redi’s first letter on vipers. In it, Redi had presented a range of possible explanations for the working of the venom, although without committing himself to one. (p.80) Fontana proposed that venom killed by destroying a fundamental principle of life: the irritability of the muscles. This explanation was, of course, not among those put forward by Redi; it could not have been. Fontana drew on the physiological and pharmacological experiments that were ongoing at the time, Albrecht von Haller’s investigations of the irritability and sensibility of tissues being the main source of inspiration.9

The work opens with a commitment to experimentalism. We have already seen that such a commitment could take quite different forms—it could be combined with a warning against deceptive appearances, as in the Saggi; it could be combined with a turn against the old systems of philosophy, as in Bacon’s Novum Organum; or it could mean a broad commitment to “matters of fact,” as in Mead’s case. Fontana’s opening statement reads: “It is agreed at present that there is no other guide in a search into natural truths, than a knowledge of facts; it is only on facts that the philosopher can hope either to establish a reasonable system, or to form a sound judgement of those already established. Observation is alone capable of dissipating the mists that envelop the hidden causes of the phenomena of nature.”10 Throughout the book, Fontana reiterated that experimentation was the road to truth, that he had performed experiments to establish this or that, that the most brilliant philosophical systems were worth nothing unless they were founded on good experiments, and so on. Fontana’s experimentalism committed him to variations of experimental designs and to tracing all the circumstances of an experimental trial.

In chapter 4, we saw that Mead’s experimentalism had a Newtonian ring to it and that, just like experimentalism more broadly, “Newtonian” experimentalism, too, comes in different flavors. Mead called for an experimentalism based on numbers, mathematics, and geometry. Haller expounded another form of Newtonian experimentalism in his treatise on irritability and sensibility. Because Haller did not want to engage in the discussion of the delicate issue of whether animals had a soul, he avoided the matter by a Newtonian move, stating that he did not wish to speculate about why some parts of the human body were irritable and others were not. The source of these properties, he said, “lies concealed beyond the reach of the knife and microscope, beyond which I do not chuse to hazard many conjectures, as I have no desire of teaching what I am ignorant of myself.”11 For Haller, being a Newtonian meant not devising any speculative hypotheses. Fontana advocated the Newtonianism of the Opticks and the Newtonianism of the Queries. Like Mead, Fontana made a reference to the “creative genius of Newton.” Unlike Mead and Haller, Fontana (p.81) pointed out that such genius was needed to derive the “causes of the laws” that regulated observations.12 As we will see later, he also followed Newton in his view that knowledge of the nature of causes was outside the realm of science.

Fontana spent more than a hundred pages putting his findings before his readers. He described numerous experiments on the nature and action of venom, and he commented extensively on experimental methods. As in the early modern writings, methods discourse in Fontana’s work goes well beyond a general commitment to experimentalism. Along the way, and as an integral part of the account of his experimental report, he offered detailed comments on proper procedure. After decades of intense observations and experiments, experimenters had become painfully aware that disagreements among observers were rather frequent—observations might be disproved by others or even by one’s own continued efforts. And disagreements were hard to resolve. It was therefore necessary to do more than just add further observations to the existing jumble of facts; it was necessary “to discriminate nicely, to compare the experiments of my predecessors with my own, to trace and develope [sic] all the circumstances of them, and in short, to discover what may have occasioned so great a variety in the opinions of these observers, and in their manner of seeing. Such is the true motive that has induced me to give an account of the experiments which follow.”13

True to his word, Fontana described not only a host of experimental trials but also all sorts of conditions, circumstances, and particulars that surrounded his experiments. The result is a bulky, somewhat tedious report showing Fontana’s readers how he had arrived at his general conclusions about the nature and working of venom.

One of the conceptual tools for the analysis of experimental reports that I introduced in chapter 1 is the analytic distinction between narrative and argument. Larry Holmes initially developed this distinction through a comparison of writings by a contemporary of Fontana’s, the mid-eighteenth-century naturalist René Antoine Réaumur, with a work authored by the early nineteenth-century physiologist François Magendie. Both scholars combined elements of narrative and elements of argument in their writings about experiment, Réaumur emphasizing narrative and Magendie argument.14 Réaumur described series of linked experiments to investigate the digestive tracts of birds. He provided many details about the experimental conditions and circumstances of the various trials, such as at what hour the experiment was performed, the forms of the tubes the birds (p.82) had to swallow and how these tubes changed shape inside the stomach, and so forth. Each modification of the experimental procedure appears motivated by the previous experiments, and at the end, the reader—now a fellow traveler compelled to agree with Réaumur—“feels that he or she has been with Réaumur through a scientific adventure.” In this sense, the descriptions of the linked experiments are an effective argument for Réaumur’s conclusions as well as a vivid story in their own right.15 Holmes reminds us, however, that even those experimenter–authors who emphasize argument incorporate narrative elements in their reports. Their account might offer a succinct, cogent reconstruction of the logical (rather than the chronological) sequence of experimental trials so as to make a point, but to be convincing, it must still refer to the course of the investigation and must give the reader a sense of what was actually done.

Fontana’s treatise is certainly not a narration of his research in the sense that it exactly follows the order in which the experimental trials were actually carried out. Nevertheless, his treatise has the flavor of a (very gruesome) scientific adventure story. The narration of the quest is interspersed with references to proper procedure, statements that are more general than the protocols for the investigation of the chemical nature of yellow fluid and of its effects on body functions. Such methodological concepts and views formed an integral part of the account of Fontana’s experiments. Like Charas before him, Fontana made it clear that his treatise did not describe every single experimental trial he had actually performed. Like Redi, he put together narrative and methods discourse to advance and argue for a position.

The self-experiments that Fontana undertook to establish the chemical nature of venom illustrate how he integrated remarks about proper procedure into the account of his experiments. Tasting substances was one of the main modes of chemical assaying in the early modern period,16 and Fontana took it on himself to taste the viper venom—“more than an hundred times.” He knew from the writings of Redi and Mead that Redi’s viper catcher and Mead and his friends had tasted it and that ingested venom was not fatal. The viper catcher had reported that the venom did not taste like much; according to Mead, however, it was acrid and pungent, as one would expect from a spiky salt. Fontana’s methodological principles—he referred to “philosophical necessity”—required that he taste the venom for himself. He tasted both the liquid and the dry powder. He found the venom insipid, as did his brave servant, who had to swallow it as well—repeatedly, of course.17

(p.83) Fontana described vividly and in great detail the taste and the feel that the venom left on his tongue: cold and insipid but not as insipid as spring water. Rather, it resembled “the almost insensible flavor of the fresh fat of animals.”18 Only if the undiluted venom remained in the mouth for a long time did it leave an unpleasant sensation, as if from something astringent. Nevertheless, Fontana declared himself unsatisfied with the evidence he had assembled. He went on to compare the taste of viper venom to that of the bee, wasp, and hornet. Again he performed self-experiments, and again he described all the sensations he experienced: the stinging and burning, the lasting pain. These experiments were done repeatedly and with variations, whereby Fontana took the venom from the stings of the insects or from the small vesicles that contained it. Finally, he fed viper venom to a dog. The animal kept licking its lips and begged for more. Evidently, it found the taste agreeable and was not in pain—another reason to conclude that venom was not acrid and fiery.

The argument against Mead is driven forward throughout the three chapters that deal with Mead’s views. At the same time, the narrative preserves the sense of an investigative journey starting with observations and experiments. Along the way, the reader learns what measures Fontana had taken to ensure proper procedure. Fontana opened the discussion by stating Mead’s initial position: that venom was an acid. He did not state his own contrary view, nor did he mention that Mead had in fact changed his position later. Fontana then presented his own experiments, which showed that venom was not an acid. Only then did he note that Mead had withdrawn his earlier claim but that Mead’s book had reached him “too late” (too late, we might assume, to prevent Fontana from engaging in a set of experiments on the acidic nature of venom). He then proceeded to note that because Mead had changed his views, he himself could refrain from trying to clear up the apparent contradiction between the outcomes of his and Mead’s experiments.

Fontana could have saved his readers—as well as the typesetters—much time had he simply stated at the outset that Mead’s and his experiments both confirmed that viper venom was not an acid. But then the reader would not have known by which investigative pathway Fontana had arrived at his conclusions, and Fontana would have had fewer occasions to demonstrate how carefully he had traced all the circumstances and to expand on the proper procedure of experimentation.

When Fontana repeated Mead’s initial simple color test, he found, contrary to Mead and to his great surprise (so he said), that the test paper did (p.84) not turn red. Instead it yellowed—that is, it took on the color of the venomous fluid. As it “appeared extraordinary” to Fontana that “so learned a man as Mead should have been deceived in so easy an experiment” he repeated it again and “that nothing might be neglected, varied the experiment a hundred different ways.”19

The notion of “many many” experiments was a leitmotif of methods discourse in Redi’s letters. In Fontana’s work, the leitmotif is the phrase “I varied this experiment in a hundred different ways.”20 It appears over and over again. In the extended critique of Mead, he could make this same point twice, first with respect to the color tests that both investigators had performed and again with respect to another issue on which he still disagreed with Mead—namely, the question of whether venom contained saline crystals with sharp points. In both cases, the reference to variations helped make the point.

What is more, Fontana told his readers exactly how he had varied his experiment. The contrast to Mead’s account could hardly be any greater. Mead simply told his readers what he (and others) had found. Fontana described what he had done. To determine whether venom was an acid, he experimented with different forms of venom. He sometimes took it directly from the viper’s tooth; sometimes he let the snake bite a piece of cotton. He used pure venom, diluted it, or mixed it with other body fluids such as saliva. But however he tried it, the paper did not turn red. He also could not observe the bubbles that, according to Mead, should appear on mixing venom with alkaline substances. Even the glance through the microscope did not give any evidence of effervescence.

Mead’s second questionable finding—the microscopic observation of sharp crystals in viper venom—also could not withstand Fontana’s scrutiny. In his search for saline crystals, Fontana even varied the instrument, using an English lens as well as a solar microscope, but as much as he tried, he could not see any crystals in the venom.

It is characteristic of Fontana that he offered an explanation (a rather unflattering one) for why Mead might have fallen into error. Mead might have looked at some bodies floating in saliva and mistaken them for salts—a mistake easily made by those who were “not very conversant in the use of the microscope” and “not well acquainted from habit with the shape of the different salts that are found in liquors.”21 Fontana also described—again, characteristically—two additional experiments he had devised to make himself “still more certain” and “to remove all doubt and suspicion on a matter so important and so generally adopted.”22 He (p.85) peered down his microscope and watched how the drop of venom cracked and fragmented from the outside inward while it was drying. He repeated this several times, both with pure venom and with drops of venom diluted with pure spring water. Almost in passing, he also mentioned that he had had witnesses, two “celebrated Professors of the University of Pisa” who had assisted with the observations and agreed with the findings.23 Only at the end of this comparatively long chapter (three times longer than the preceding ones) did Fontana announce that he was now sure that no salts were to be found in viper venom. He had “seen the theories founded on this principle, to explain the action of the viper’s venom, fall and vanish before experiment, which proves that no salt, either acid, alkaline, or neuter, exists in this humour.”24 How could anyone doubt this conclusion?

A Hundred Different Ways of Making an Experiment

Fontana’s other key insight—the explanation of the working of viper venom—is also supported by a detailed report of an investigative journey. In hindsight, it is obvious that Fontana relied heavily on Haller’s distinction between two kinds of body parts—those that were irritable and those that were sensible. This distinction was one of Haller’s major contributions to the study of life.25 In his famous work on the irritable and sensible parts of animals from 1753, Haller derived the two concepts from physiological experimentation on animals: He called “irritable” all those tissues that contracted on being touched and “sensible” those parts that when touched transmitted an impression to the soul.26

Fontana’s experiments showed that viper venom, just like other poisons such as opium, napel (Aconitum napellus—used in cooking as a meat tenderizer), and mephitic air, made muscles flaccid, livid, and putrid.27 The body parts of people who had been bitten by vipers became paralyzed, again suggesting that irritability was compromised. Fontana procured “fifty of the strongest and largest frogs” and had each bitten by a viper, “some in the thigh, others in the legs, back, head, &c.”28 Some of the animals received a drop of venom through a wound Fontana had made with a lancet. Some frogs died very quickly, others after several hours, and others not at all. But there was one significant common feature: All animals suffered the loss of their muscular force after having been bitten or wounded and treated with venom. Stimulating and pricking the muscles and limbs of the dead animal produced no effect, even though in some cases, the heart (p.86) still continued to beat. Like opium, napel, and mephitic air, viper venom made the body parts lose irritability, that “grand principle, both of voluntary and involuntary motions in the animal economy.”29

This interpretation of the findings is clearly informed by Haller’s ideas. What is more, Haller’s work inspired Fontana’s methodological views. Haller expounded several methodological rules for experimentation along with his experiments on sensible and irritable body parts. He did so not because he had taken an innovative approach to experimentation. He noted that he was “obliged to repeat and multiply” his experiments to prevent himself from “falling accidentally into any mistake.” He declared that he had “examined[,] several different ways, a hundred and ninety animals.” The strategy itself is not revolutionary. The novelty was in the results Haller advanced—because these results were so revolutionary, he had to be “very exact” in his proofs.30

The parallels between Haller’s and Fontana’s methods discourse are striking. Still, it would be rash to assume that Fontana simply borrowed the formulas offered by Haller or by Redi before him. Unlike the young Mead, who had couched his views on venom in the language of mechanical philosophy, Fontana ended up making Redi’s and Haller’s methods discourse his own. We will see in the next chapter that the French treatise on viper venom is not merely more methodologically reflexive and explicit than the Italian treatise but also much more specific about the various practical challenges Fontana encountered. The level of engagement with practicalities and the concern with identifying the sources of other people’s errors suggests that Fontana’s methodological views were shaped and sharpened by encounters with the complexities of experimental settings.

At the end of his first book on venom, Fontana announced: “Unless I am deceived, I have now, I think, happily terminated the controversies that have so long kept people at variance, on the mode of action of the venom of the viper.”31 This declaration was premature. As Fontana continued his studies on viper venom in the hopes of finding an effective antidote, a host of new questions opened up, and he continued to devise experiments. Because his research remained inconclusive, Fontana refrained from publishing any of it for some time, and he also delayed the publication of the French translation of the Italian book.

Notes:

(1.) Klauber, “Foreword,” 1. As we will see, this description is highly problematic. I mention it here only to illustrate that Fontana’s methods were considered striking and worthy of mention even into the mid-twentieth century.

(2.) For details on Fontana’s life, education, and works, see the rich intellectual biography by Peter Knoefel, Felice Fontana: Life and Works (Trento, Italy: Società di Studi Trentini di Scienze Storiche, 1984). For more information about Fontana’s involvement with the Florentine Museum of Natural History La Specola and specifically with the collection of anatomical wax models, see Anna Maerker, Model Experts: Wax Anatomies and Enlightenment in Florence and Vienna, 1775–1815 (Manchester, UK: Manchester University Press, 2011).

(3.) Unlike Mead, Fontana did not provide a general account of poisons. The parts of his treatise that deal with poisons other than viper venom are not elaborated. But he did draw analogies between the working of animal and vegetable poisons, and he followed very similar principles in his experiments.

(4.) For details on the publication see Knoefel, Felice Fontana: Life and Works, 267–68.

(p.247) (6.) In the following, I will refer to the Italian and the French treatise as the two “books” or two “treatises” on viper venom. The “two volumes” are the two separate printed works. In other words, Fontana’s second book on viper venom is printed partly in Volume I and partly in Volume II.

(7.) The quotes are from the English translation of 1787.

(8.) Anatomia animataShirley A. Roe, “Anatomia Animata: The Newtonian Physiology of Albrecht von Haller,” in Transformation and Tradition in the Sciences: Essays in Honor of I. Bernard Cohen, ed. Everett Mendelsohn (Cambridge, UK: Cambridge University Press, 1984), 273–300.

(9.) Knoefel notes that Fontana was introduced to Haller’s work by his teacher Leopoldo Caldani, who also conducted research on irritability. Caldani corresponded with Haller and sent him reports of Fontana’s research; see Knoefel, Felice Fontana: Life and Works, 14–15.

(10.) Fontana, Treatise on the Venom of the Viper, I, 1–2. The Italian text uses the words osservationi and esperienze in a broad sense.

(11.) Albrecht von Haller, A Dissertation on the Sensible and Irritable Parts of Animals (London: Printed for J. Nourse at the Lamb opposite Katherine-street in the Strand, 1755), 2.

(13.) Ibid., 2.

(14.) In his later essay on argument and narrative in scientific writing, Holmes’s example for “argument” is Denis Dodard’s memoir on chemical experiments performed at the Paris Académie des Sciences in the late seventeenth century. Dodard discussed “in logical rather than chronological sequence the various methods that the Academicians had learned to employ, over the years, to identify the products of their distillation analyses”; see Holmes, “Argument and Narrative in Scientific Writing,” 168–69.

(16.) Evan Ragland, “Chymistry and Taste in the Seventeenth Century: Franciscus Dele Boë Sylvius as a Chymical Physician between Galenism and Cartesianism,” Ambix 59 (2012): 1–21.

(18.) Ibid., 56.

(19.) Ibid., 43.

(20.) This is a shift of emphasis, not a change of approach. Redi also varied his experiments, but the emphasis in his case was on many repetitions.

(22.) Ibid., 51, 52.

(23.) Ibid., 53.

(p.248) (24.) Ibid., 54.

(25.) Hubert Steinke, Irritating Experiments: Haller’s Concept and the European Controversy on Irritability and Sensibility, 1750–90 (Amsterdam: Rodopi, 2005).

(26.) Haller proposed to call “that part of the human body irritable, which becomes shorter upon being touched, very irritable if it contracts upon a slight touch, and the contrary if by a violent touch it contracts but little.” By contrast, a “sensible” part of the human body is one that “upon being touched, transmits the impression of it to the soul.” Because it was not clear whether animals had a soul (or because he did not want to take sides on this sensitive issue), Haller ultimately based the distinction on the behavior of the animal as it could be observed in experimental contexts. He called “those parts sensible, the Irritation of which occasions evident signs of pain and disquiet in the animal. On the contrary, I call that insensible, which being burnt, tore, pricked or cut till it is quite destroyed, occasions no sign of pain nor convulsion, nor any change in the situation of the body. For it is very well known, that an animal, when it is in pain, endeavours to remove the part that suffers from the cause that hurts it; pulls back the leg if it is hurt, shakes the skin if it is pricked, and gives over evident signs by which we know that it suffers”; Haller, A Dissertation on the Sensible and Irritable Parts of Animals, 4–5.

(27.) Mead considered a similar group of substances.

(29.) Ibid., 100.

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