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

these things are enveloped in such shadows that the spectator feels compelled to admire phenomena whose cause is unknown, and perhaps will remain unknown. Whether these are effects of one cause manifesting itself differently in different parts, or not? I willingly suspend judgment on that, as is appropriate for a youth, and I look solely to sensibility and irritability, established by so many experiments, especially those of the immortal Haller, in which the cause of every motion and sensation, and therefore of the diversity of temperaments (§ 7), undoubtedly resides for the most part.

§. 9.

For not the same degree of irritability and sensibility is given to all by nature, and this innate diversity seems to arise from a collection of many causes, which we certainly do not yet all know, but of which, if I may put them forward, the following are easily the principal ones:

a) The tension or relaxation of solid parts, and their increased or diminished elastic force.

Surgery will teach us with very many examples that irritability and sensibility are greatly increased by the tension of parts e; however, it cannot be doubted that elasticity is also excited by the same tension to exert its own force more f.

b) The diversity of the nervous system.

Perhaps the different relative proportion of the brain and nerves observed in various kinds of animals g and between Europeans and Ethiopians h has a place in any individual men whatsoever. But since that proportion of nerves and brain is not found in the elephant i, and therefore that specious observation of the Illustrious Soemmering is not free from all doubt, it seems to me both most likely and more suitable for demonstrating the matter if one considers not only the volume of the brain and nerves, but also their mass, that is, their specific weight. From this diverse proportion of nerves and brain in individuals of the human race, remarkable illustrations regarding innate sensibility could be expected.

When we attend to the great thickness of the nerves in animals of cold blood, to their great vital force appearing even in parts severed from the brain, we are at least led into the suspicion that a greater nervous energy, not depending on the brain k, is proper to the thick nerves of humans than to the thinner ones, and because of this power of the nerves free from the sensorio communi common sensorium/central sensory seat, it is sufficient to excite the muscles, but with...

e) Illustrious Richter, Fundamentals of Surgery, Vol. I, p. 4, 239.
f) Cl. F. Fontana, Philosophical Researches on Animal Physics, Florence 1775, p. 7.
g) Ebel, Neurological Observations from Comparative Anatomy, Traiectum ad Viadrum, 1788.
h) Illustrious Soemmering, On the Physical Differences of the Moor from the European, Frankf. and Mainz, 1785, § 62.
i) S. I. van Geuns, Medical Questions, Harderv. 1790, p. 33.
k) A. Monro on the nervous system, Edinburgh and London, 1783, Ch. 8. Illustrious Blumenbach’s Physiological Institutions, § 213.