Laws of Animality

Appendix 1. (1880).

Brown undertook to prove that all animal phenomena depend on the single property of excitability. His argument is as follows: 'The effect of stimuli on excitability is always the same because it always consists in promoting sense, muscular motion, thinking activity and the affections of the soul.' It seems almost impossible that such a brilliant man as this Scottish doctor could confuse four things so different and opposite. But it is even stranger to find so many disciples of his who have never even suspected the mistake contained in such a gross sophism. Amongst Italian doctors, Guani pointed out, in opposition to Brown, that not all organs manifest uniform effects as a result of the action of external stimuli (Risposta al tema pubblicato dalla società italiana delle scienze residente in Modena, Modena, 1821).

This objection was reproduced and perfected by Bufalini: 'In the first place, Brown always maintains excitability as one and the same because (he says) the same effect always follows the action of the stimuli. This effect is sense, muscular motion, thinking activity and the affections of the spirit. But here he confuses abstraction and reality. Making these vital acts the same depends solely upon their common, abstract attribution: that of being governed by the laws of life. But in reality, sense is certainly not the same as muscular motion which, in turn, is not the same as mental actions, and so on. Indeed, because all these vital acts are different, and because the same external agent acting on the nerve excites sense, promotes muscular contraction in muscles and arouses mental actions in the brain, we must necessarily grant different kinds of excitability in the nerve, muscles and brain where these vital acts can be present through the simple action of excitability itself' (op. cit., Memoria, Modena, 1823, f. 16).

He shows clearly that if excitability were the same property in the different parts of the machine, and differed only in quantity, an increase of stimulus (on which this quantity depends) in a muscle would mean, for example, providing it with sensation, which cannot be done. However, Bufalini himself is unaware of the main, overriding argument illustrating the fallacy in Brown's work. This argument depends on the absolute, essential difference between the subjective phenomena of sense, affections and thought, and the extrasubjective phenomena of muscular motion. Bufalini grants the existence of different excitabilities proper to different parts of the body. In virtue of these excitabilities, the external agent promotes motion in muscles, sense in the nerves and thought in the brain! Now, motion is undoubtedly produced by external agents in all parts of the body, in the muscles, the nerves and the brain itself (although the motion produced in one of these organs can differ from the motion produced in another in direction, rapidity and frequency, etc.).

But these are merely accidental modifications of motion, as we know from extrasubjective experience which, however, does not tell us that the external agent producing motion in the muscles also produces sense in the nerves. Even less does it inform us that the external agent produces thought in the brain. It simply indicates that this agent produces motion in nerves, brain and muscles, a motion which is an effect analogous to the nature of the agent, but nothing more. Another subjective, internal experience is present which tells us simply that when the external, extrasubjective agent acts in the extrasubjective body called 'nerve' and has produced a certain motion, sensation is manifested in the subject itself. This subjective experience is so different from the previous experience that properly speaking it does not and cannot witness anything of the extrasubjective phenomena of motion which the external agent produces in the nerve. It simply witnesses to mere sensation. What we have to do, therefore, is to compare the two experiences, the extrasubjective experience which shows motion produced by the external agent, and the subjective experience which presents us with sensation, in order to know that the space in which sensation expands is identical to the space where the corresponding motion originates.

The external agent is so incapable of producing sensation that it does not even exist relative to the faculty which denotes sensation. Hence motion and sensation are effects of specifically different potencies. The phenomenon of motion is even less like that of sensation than taste is like gravity.

Because motion and sensation are effects of different faculties, we have to ask to which of these faculties the external agent pertains. Now, as I said, the external agent pertains to the faculty which enables us to know motion, not to that which enables us to know sensation. It pertains, I mean, to the faculty of extrasubjective experience, not to that of subjective experience. All that we know, therefore, of the external agent is given to us by the faculty which enables us to know motion. This faculty tells us that the external agent is the cause of motion but does not tell us anything about sensation. We cannot say, therefore, that the external agent is the cause of sensation. On the other hand, the faculty of subjective experience which witnesses to sensation tells us nothing about the external agent and hence cannot indicate the cause of sensation itself. It is, therefore, a gratuitous and obviously false assertion that the external agent as applied to the muscles promotes motion there, or as applied to the nerves promotes sensation.

It is even more inexact to say that the external agent applied to the brain promotes thought in this way. To demonstrate this, it is sufficient to observe that thought cannot be aroused by any external agent which does not first arouse sensation, the sole excitatory of thought. Now, we have seen that the external agent does not immediately arouse sensation; its proper effect is simply mere motion. Indeed, it produces only certain motions in the nerves. These motions are accompanied by the phenomenon of sensation which, however, is due neither to the external agent nor to the excitability of the fibres but to another, subjective entity, in a word, to a fundamental feeling with its own proper excitability essentially different from that of the fibres. The external agent, therefore, is wholly incapable of producing thought in the brain. Note that internal observation shows the presence of thoughts which need neither sensations nor images. These are pure thoughts, totally unconditioned by the action of any corporeal organ.