XIII.] THE BIOLOGICAL SCIENCES AND MEDICINE. 339 



But though, as I think, there is no doubt that 

 Descartes was the first to propound the fundamental 

 conception of the living body as a physical mechanism, 

 which is the distinctive feature of modern, as con- 

 trasted with ancient physiology, he was misled by the 

 natural temptation to carry out, in all its details, a 

 parallel between the machines with which he was 

 familiar, such as clocks and pieces of hydraulic 

 apparatus, and the living machine. In all such 

 machines there is a central source of power, and the 

 parts of the machine are merely passive distributors of 

 that power. The Cartesian school conceived of the 

 living body as a machine of this kind; and herein 

 they might have learned from Galen, who, what- 

 ever ill use he may have made of the doctrine of 

 " natural faculties," nevertheless had the great merit 

 of perceiving that local forces play a great part in 

 physiology. 



The same truth was recognised by Glisson, but it 

 was first prominently brought forward in the Hallerian 

 doctrine of the "vis insita" of muscles. If muscle 

 can contract without nerve, there is an end of the 

 Cartesian mechanical explanation of its contraction by 

 the influx of animal spirits. 



The discoveries of Trembley tended in the same 

 direction. In the freshwater Hydra, no trace was to 

 be found of that complicated machinery upon which 

 the performance of the functions in the higher 

 animals was supposed to depend. And yet the hydra 

 moved, fed, grew, multiplied, and its fragments ex- 

 hibited all the powers of the whole. And, finally, 



