1Messieurs,

2Stahl’s1 medical theory or physiology is contained in a publication titled Theoria medica vera, printed for the first time in Halle in 1708.2 Juncker,3 his chemistry pupil, whom we will study as a physiologist, presented another edition. Stahl attributed ordinary and extraordinary body phenomena to the soul, as we understand it, as the principle of sensitivity, reasoning, and willpower. The Ancients used the word soul to designate any principle of internal motion: some philosophical sects recognized a soul of the world that moved all parts of the universe in regular order; a vegetative soul that was the internal principle of the motions of plants, bringing the sap up through their tissues to develop leaves and fruit; a third soul called sensitive, common to all animals; and finally a reasoning soul unique to man. Advances in philosophy brought better ideas, potentially expressed in a more specific way. The ability to feel came to be considered as distinct from the capacity to move our muscles, the capacity to conceive ideas and to combine them to form arguments. Some, called idealists, even assumed that nothing existed beyond the existence of self, the only source of self-awareness. Body was only a vain appearance, some sort of a dream of the soul. Others, designated by the term materialists, attributed existence solely to matter, and recognized that internal and external body motions, our feelings, our ideas, and our voluntary acts based on these ideas were only modifications of matter. A third system taking from the former two recognized the existence of the matter as real and assumed that the principle experiencing sensations, forming ideas and combining them to draw conclusions, and making the body execute motions should be specifically called the soul in a defined acceptation. This system led to the difficulty of determining how a principle distinct from the body would act on the body and how the body acted on the soul. There were various opinions. Leibniz,4 for example, rejected the action of the body on the mind and the mind on the body and admitted that both experienced parallel and analogous changes. This system is known as pre-established harmony. Other philosophers, like Malebranche,5 assumed that the action of the mind on the body, and vice-versa, was not the result of either one but of divine intervention. All these and other hypotheses do not matter. I only repeat them here to facilitate our understanding of Stahl.

3According to this physiologist, who starts from the principle of Descartes’s philosophy,6 no spontaneous motion could exist in matter. If there were a general motion of the world, this motion was determined since the origin by the Creator. All specific phases compounding the motion are the result of the difference of shape of all the parts of the matter. There cannot be a new motion without an immaterial being producing it. Because vital motions are not all communicated motions, as they do not all result from the general mass of motion animating the entire creation —some spontaneously start from an action of our willingness, for instance, when we suddenly and freely go from a state of rest to agitation, or even in the most violent state (a change that materialists had to attribute to anterior motions executed in the whole universe)— Stahl placed in the soul the cause of all motions produced in the body, without the soul even realizing it. The mode of action of the soul on matter is an unexplained difficulty but this difficulty is not specific to Stahl’s system and also exists in Descartes’s. Stahl, who considered that matter had no active force and that organization had a determined goal, considered the soul as the source of all voluntary and involuntary body activities and even claimed that the soul was building the body inside the mother with the available matter. According to him, the soul feeds adequately each part, determines the direction and distribution of fluids, operates the secretions, and sends the adequate particles to each point. He explained the effect of a woman’s imagination on the fetus, which was not the subject of any doubt at the time. The alleged animal minds, which according to Descartes were the almost essential source of the motions of the living body, are totally rejected by Stahl. According to him, the soul does not need them as instruments because it is immediately present in all parts of the body. It is extended; its activity is divisible, meaning that it can act a certain way on a point and another way on another point. However, he considered the pineal gland7 as the center of its substance.

4According to Stahl, the efforts of nature during our illnesses, efforts recognized by all doctors and noticed even by Hippocrates and later by Van Helmont8 who attempted to justify them with the archeus,9 are reasonable motions to repulse the causes of illnesses and attempt to repair earlier mistakes. The soul often performs similar efforts to repair the effects of ignorance of doctors. If Stahl is asked to explain how the soul could perform such acts without awareness, he answers that it acts without clear ideas, with a sort of instinct and habit. It is certain that we do a lot of motions, and even complicated ones, without realizing it. In each motion, we involve a multitude of different muscles ignored by all, except by anatomists. But it can be answered that it takes long to execute even the simplest motion, with the exception maybe of the first motion of breathing and suckling and of those determined by irritating causes. A child needs to learn, so to speak, all his movements. It is not through a study of the muscles or by repeated trials that he can ascertain their use. Animals also need a certain experience; nobody ignores that small birds, for example, flap their wings and practice at the edge of their nest before flying away.

5To support Stahl’s doctrine, we can give the example of a man playing the piano. This man has to recognize the notes in his notebook and put each of his fingers on a special key at a determined speed. In an almost indivisible instant, he has several ideas and sometimes simultaneously executes extremely large numbers of voluntary motions requiring a lot of precision. Otherwise, he would play out of tune or poorly. The same applies to dancing and other actions requiring very complicated movements, executed without thinking. In some cases, these movements are not only the reflection of a feeling but require multiple thoughts: this happens when we defend ourselves by making weapons or when we read. In reading, we have to be aware of the shape of letters, of the sound they represent according to the language of the book, and at the same time of the meaning of the different words in order to read correctly. All these actions happen so quickly and indivisibly that no one realizes or remembers the multitude of the prerequisite small feelings, small thoughts, and small consequences. This is even more tangible in writing than in reading. Someone who writes under dictation must remember the spelling rules that are so often arbitrary and vary according to languages in a way that the same sound is almost always expressed using different letters.

6Stahl used these various phenomena to assert that the soul could execute countless movements unknowingly. But, as I already did, it should be replied to Stahl that all motions he cited to support his doctrine are learned motions. Before writing rapidly under dictation or on his own inspiration, a man has to learn the spelling rules, the order of letter placement to form words. It requires a practice of several years to master and rapidly use this knowledge. Such talent is nothing extraordinary. There is no reason for the mind, under the same rules of motion as matter, to not be able to devise and produce thousands of ideas within a time frame that seems almost indivisible for body movements.

7The shortest time, physically speaking, is still intellectually divisible ad infinitum, in the same way as the smallest space. The opposite is believed because of our speed of action, out of habit, in the examples I gave. We do not realize and remember how our mind works. We only remember the actions we execute slowly. We rarely remember words spoken rapidly and we would not even remember a speech hastily prepared. The facts invoked by Stahl are inconclusive. It cannot be implied that the soul instinctively acts on all body movements and that before getting a body, it enters inside the mother to distribute the bodily components without any prior knowledge and any idea of its objective. All of Stahl’s efforts are in vain in this context even if his principle is not as vague as Van Helmont’s archeus.

8Stahl’s strange idea of conceiving the soul as the principle forming the body, directing the circulation and alternatively constricting and dilating the heart, directing stomach digestion and pushing the bile back to the duodenum to finish digestion, defending the body like an army general every time the enemy appears in the form of sickness, this strange idea had a certain fame because it was a formula to explain all physiological and pathological facts. Physicians, therapists, pathologists, the multitude, everybody in one word, appropriated the idea as the rule of conduct because ordinary physics did not chart all phenomena.

9According to Stahl, the instrument used by the soul for its actions is tonic motion, the tension of body parts. Tonic motion became a general term in the language of the physicians in Stahl’s school. There is an analogy with Glisson’s10 irritability, developed by Hoffmann11 and Haller.12 The difference is that irritability is a property of organized matter, exerted by stimulants or irritants regardless of the soul. In Stahl’s system, soul is the source of tonic motion. If Stahl was asked how soulless plants could live, he was forced to admit that external physical forces were enough for their development and therefore that they had a germ facilitating the action of such external forces. This thoroughly ruined his doctrine because if this germ existed for plants, there would be no reason not to admit something similar for animals.

10Stahl’s followers amplified his ideas and took them further. One of them, Daniel Gohl, a Berlin physician, published in Halle in 1739 a work in German: Thoughts on Minds Free of Prejudice and Particularly the Nature of Animal Minds.13 The Stahlian efforts had the objective of overturning the system of minds introduced by Descartes. According to Gohl, there is a plastic principle directing the formation of the embryo, a sort of vegetative soul. This soul acts based on innate ideas and before the development of reason. He compares it to the capacity of insects to build admirable structures without us imagining that they applied reasoning. The bee, for example, builds a rather complicated structure, ingenious and corresponding to the most exact geometry even if it does not know any principle of this science. Gohl imagined that the plastic principle he recognized had the innate idea of the work to be performed and that it acted based on this idea in the same way as a mason builds a house based on plan he has in his mind. According to Gohl, nerves are not hollow and do not steer minds of animals. Soul influences them by exerting a tension. This tension is not spread inside the body but lies in the brain from where it influences all parts of the body. Even menses are subjected to its will.

11Juncker also adopted Stahl’s ideas and gave them the most elaborate order. We already mention him as a chemist.14 He published a work titled Conspectus physiologiae15 in which he expresses the opinion that pure intellect influences, without awareness or feeling, all bodily phenomena. On the other hand, he claims that intellect or soul predicts what will happen to the body and acts to prevent plethora, which is obviously contradictory.

12Michael Alberti,16 another follower of Stahl, was born in Nuremberg in 1682, taught in Halle in 1710, and died in 1757. He published, as it was the custom, a multitude of theses on the Stahlian doctrine. His main work was called Nova Paradoxa or Treatise on the Soul of Man and Plants.17 Alberti pushes the superstition to the point of saying that he was often warned by sneezing of the arrival of his friends or of letters. It was easy to go from the Stahlian system to mysticism and to all absurdities created by superstition. At the time, many physicians believed this superstition and the links between the human soul and the general phenomena of the universe. It could even be said that pantheism dominated some schools and up to a certain point entire countries. According to Alberti, animal souls are immortal like the human soul and can also commit a sin. He claims that the father loses weight at the highest growth of the fetus, which he fixed at eight months, and that from that point on, the fetus develops at the expense of the father. You see to what madness we can get through the system of direct intervention of the soul on bodily motions for which we do not know the cause. Friedrich Hoffmann, Stahl’s predecessor, always expressed opposite views.

13Leibniz first attributed its own energy to matter. He then adopted the theory of Glisson and other earlier philosophers from the seventeenth century to gradually reach the Hallerian irritability, a view as rational as Stahl’s idea was superstitious and mystic. Leibniz’s ideas prevailed and after fifty years, Stahl’s ideas fell into oblivion. However, Leibniz’s doctrine spread very slowly in England and in France. In England, some philosophers combined the ideas of Stahl and the iatro-mathematicians, which is understandable. George Shell,18 born in 1671, a pupil of Pitcairne,19 and a physician in Basel and London published in 1725 a book presenting this combination: De natura fibrae.20 As Pitcairne did, nerve fibers were considered from a mathematical point of view in the book. The author claimed that soul even influences the motions we call involuntary. To support his assertion, he cites among other examples the case of a colonel named Tompshin21 who could momentarily stop his heart beat, particularly at the end of his life. While such power of the will is very rare, Shell draws a general conclusion that is certainly false.22 Like Gohl,23 he assumes that that soul is at the origin of the nervous system, that it can transfer its will to the nerves like an organist transmits the action of compressed air by pressing each key.

14In England, the author who spread Stahl’s doctrine the most was Frank Nicholls,24 a lecturer and anatomy professor at Oxford. He is famous for his injections, similar to Ruysch’s.25 In a book called De anima medica proelectio printed in 1750,26 in which he fights and heaps invective on the anti-Stahlians, he even claims that the soul influences not only innate ideas but has also passion and politics. Therefore, the soul gets angry when a physician upsets it by using unsuitable remedies and preventing it from doing what is necessary to heal the body. In this case, it can even get angry to the point of abandoning the poor person to the fate brought by the physician. Sometimes, it acts in a more political manner: it manages to spare itself. In the case of a smallpox outbreak, it manages to drag the illness over several days so that it does not weaken too suddenly, or, when a child dies, the wet nurse loses her milk. Finally, sick patients are in a state of despondence when the soul does not know what to do anymore. Powerless, it stays idle. Despondence is always inauspicious. According to Nicholls, body decay is the result of the departure, the absence of the soul but it leaves a bit before, when it predicts that the body will decay in order to avoid the inconveniences of such an unpleasant home. It is certain that Nicholls was one of the most extravagant authors of the Stahlian School.

15Porterfield27 and Robert Whytt28 also carried the principles of Stahlianism but in a moderate way, restricted within limits that do not completely exceed the bounds of reason. William Porterfield authored a treatise on the eye,29 published in Edinburgh in 1759, which was very remarkable at the time. He claimed that pupils move by will, shrinking under bright light and dilating in the dark in a way that the impression of the retina remains the same in both cases. We do not know this by ourselves; we have no sensation or awareness and only learn by seeing the eyes of others. It is certain there is something voluntary in its variations as shown by the experiences of Spallanzani30 and Fontana:31 a cat immersed in water dilates its pupils at an extraordinary degree even if it is in full light. Therefore, it is assumed that the soul influences the vision organ because the fear felt by the cat is a feeling of its soul. This fact might be the strongest argument in favor of Stahlianism. Physiologically, it can be explained by the relationship between the choroid and the retina but this is a question that should be addressed separately.

16Robert Whytt, a professor in Edinburgh who died in 1766, presented an essay in English on the involuntary motions of animals.32 He considered the soul as the general cause of muscle contraction, determining our impressions of pleasure and pain, and acting in sleep without thinking or forecasting the future. It also influences convulsions through the nerves and even in the muscles detached from the body. It is difficult to imagine how he conceived the latter. He had to imagine that the soul is distributed throughout the entire body, the fragments of which would be torn at the same time as the muscle parts, which is a very different view from the original Stahlianism. A powerful principle is certainly needed to produce the specific motions of all parts of the body but the use of the word soul to express this general principle is an abuse of terminology. It would have a very different meaning from the usual one.

17Stahl had other followers in England but they did not present any specific forms of his system and will not be mentioned here. French Stahlians took another route and used more abstract and more general forms. Soul changed its name, resulting in the system of vital principle that, while always keeping the same name, almost always changed form. In our next session, we will present the history of this system in France and will start with the irritabilists.