[37] Mechanical Account of Poisons, 1702.
It is not necessary for us to dwell longer on this subject, or to point out the total insufficiency of the mere mechanical physiology. The iatrochemists had neglected the effect of the solids of the living frame; the iatromathematicians attended only to these[38]. And even these were considered only as canals, as cords, as levers, as lifeless machines. These reasoners never looked for any powers of a higher order than the cohesion, the resistance, the gravity, the attraction, which operate in inert matter. If the chemical school assimilated the physician to a vintner or brewer, the mechanical physiologists made him an hydraulic engineer; and, in fact, several of the iatromathematicians were at the same time teachers of engineering and of medicine.
[38] Spr. iv. 419.
Several of the reasoners of this school combined chemical with their mechanical principles; but it would throw no additional light upon the subject to give any account of these, and I shall therefore go on to speak of the next form of the attempt to explain the processes of life.
Sect. IV.—The Vital-Fluid School.
I speak here, not of that opinion which assumes some kind of fluid or ether as the means of [186] communication along the nerves in particular, but of the hypothesis that all the peculiar functions of life depend upon some subtile ethereal substance diffused through the frame;—not of a Nervous Fluid, but of a Vital Fluid. Again, I distinguish this opinion from the doctrine of an immaterial vital power or principle, an Animal Soul, which will be the subject of the next [Section]: nor is this distinction insignificant; for a material element, however subtile, however much spiritualized, must still act everywhere according to the same laws; whereas we do not conceive an immaterial spirit or soul to be subject to this necessity.
The iatromathematical school could explain to their own satisfaction how motions, once begun, were transferred and modified; but in many organs of the living frame there seemed to be a power of beginning motion, which is beyond all mere mechanical action. This led to the assumption of a Principle of a higher kind, though still material. Such a Principle was asserted by Frederick Hoffmann, who was born at Halle, in 1660[39], and became Professor of Medicine at the newly established University there in 1694. According to him[40], the reason of the greater activity of organized bodies lies in the influence of a material substance of extreme subtilty, volatility, and energy. This is, he holds, no other than the Ether, which, diffused through all nature, produces in plants the bud, the secretion and motion of the juices, and is separated from the blood and lodged in the brain of animals[41]. From this, acting through the nerves, must be derived all the actions of the organs in the animal frame; for when the influence of the nerve upon the muscle ceases, muscular motion ceases also.
[39] Spr. v. 254.
[40] Ib. v. 257.
[41] De Differentiâ Organismi et Mechanismi, pp. 48, 67.