Commentary on Human Temperaments as They Depend on the Structure and Fabric of the Body

ON THE TEMPERAMENTS OF MEN.

But this motion, especially in the animal kingdom, cannot be explained from the laws of physics known thus far; and all principles concerning the weight and expansion of air, capillary and communicating tubes, etc., do not even remove every difficulty in the vegetable kingdom z. For explaining animal motion, however, the entire series of principles that mechanics, statics, hydrostatics, and hydraulics provide is by no means sufficient. We shall always find gaps unless we return to a certain vital force—called differently by others—the primary cause of all vital motion; it is of such a nature that it never acts unless excited by some stimulus. Just as, conversely, no part of the body will make a vital motion if it lacks the faculty of receiving a stimulus, which originates from the vital force, or, as Gaub a calls it, the faculty of sensing. There exists in the nature of things an almost innumerable supply of stimuli that are able to arouse the action of the vital force. Not only the humors by which we are nourished, and by which all the vessels of our body are filled, and the whole of nature that surrounds us, affect our living solids like a stimulus, but the soul itself at every moment, according to the diversity of its own motions, irritates our solids more or less and impels them to motion, to such an extent that in the human body there is a continuous stimulus and a continuous motion.

Another effect of the vital forces, and one of no less importance, is seen in so-called sensibility, which, although it does not indeed constitute the proximate cause of vital motion, nevertheless holds wide command over the nerves and becomes the most manifest witness of the soul's interaction with the body. It acts perpetually, conveying the body's changes to the soul and, in turn, spreading the mind's emotions and commands through the body, and can be called the mother of all sensations.

Therefore, it should not seem strange that humans, endowed with these forces, do not show the same sensations and the same motions if they are exposed to different stimuli. But to observe such great diversity of sensations and motions everywhere among humans, even if they happen to live in the same conditions, remains a most pleasant and always singular phenomenon of human nature for the observer. This diversity of sensation and motion distinguishes one human from another, and all other variations of the human body, other things being equal, are nothing but the effects of a different vital force. I do not doubt that the temperaments of the human body consist solely in that diversity; for the trifles of the ancients regarding the causes of temperament to be drawn from Astrology and Chemistry have been refuted, and if any opinion required further refutation, it would undoubtedly be that which locates the proximate cause of temperament either in the blood or in the soul. — Blood, indeed, from the mother to the fetus...