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

passing to the fetus could contain a greater or lesser stimulus, and could irritate the heart as well as the vessels to more or less vivid contractions; yet, I admit only with difficulty that the mother's blood is the cause of the newborn's temperament, since so many examples exist and are well known to me where children, and even more tellingly, twins born of the same mother, differed greatly in temperament.

If, indeed, the cause of temperament were to be sought in the blood, it must necessarily be sought in that which comes from the mother, since later on the elaboration and mixture of the blood depend upon the action and motion of the solids, and therefore it cannot be the primary cause of a diverse temperament.

b) Brief Treatise on Temperaments. Schafh. and Frankf. (Edited by Peyer 1760.)

Let us return to the second question: can the cause of temperament be located in the diverse functions of the soul? Since many authors, among whom I wish only to name the excellent Kaempf b, have looked upon the differences in temperament as referring solely to the diverse properties of the soul, with almost no consideration for the body, I believed it not useless to dwell here a little while. Not occupied by a prejudiced opinion, I am led by no desire more ardent than that of finding the truth; but so that I may not stray from the straight path, certain general principles must be set forth first.

The soul of man is endowed with two supreme faculties: namely, sensing and understanding. The former, or intuitive, is passive, and it receives only the impulses brought through the so-called sensory organs, and is affected and moved by them. The latter, however, is active, and it digests, connects, dissolves, and compares the intuitive ideas suggested by the senses, and gathers new ones from them. If the faculty of sensing, therefore, receives no impressions except through the sensory organs, it is also clear that it depends as much as possible upon the condition, or capacity, of the nerves to receive stimuli. Whether the soul’s faculty of sensing itself is different in different men, or whether all those diversities of sensations in different individuals—the soul's faculty of sensing being posited as the same—can be explained by the diverse condition of the nerves, I shall not decide. However, it seems likely to me that the soul's faculty which I have called active depends more upon the structure of the encephali the brain than upon the irritability and sensibility of other parts of the body. I believe that the nerves, for whose faculty of sensing the soul's power can be quite diverse according to their different sensibility and condition, have little efficacy regarding the faculty of understanding; since in this faculty, it is more a matter of the way in which perceptions and ideas are combined, ordered, and compared, than of the vehemence of perceptions or of the greater or lesser value of the external senses by which ideas are brought to the soul. Memory, fantasy, judgment, and so many other faculties of the soul...