2 



FORMER VIEWS ON THE CAUSE 



Anaxagoras defined an animal as an automatic machine, but 

 he left undecided what cause moved the machinery. Socrates 

 ridiculed this idea even on his death-bed. 1 ) According to Ari- 

 stotle the animal motions and animal heat are intimately con- 

 nected ; the heat is produced by the food. The heart is the 

 centre of motion and sensation, has a life of its own, and is the 

 hottest part of the body. 2) Plato considered the red color of the 

 blood as an effect of the life-fire, and the blood itself as the 

 bearer of the vital force, as the seat of the soul. 3 ) The Pytha- 

 goreans defined animal life as the result of the entrance of 

 the "life-spirit" into the body 4) by the respiration-process, 

 and declared the brain to be the seat of sensation. — As 

 the scientific development ceased in Europe for a very long 

 time, we do not find any discussions upon this subject up 

 to Descartes, who in the year 1637 expressed his conviction 

 that all the forces of nature consist in certain motions of the 

 molecules ; the animals were in his opinion caloric automatic 

 machines, in which the motions of the blood and of the organs 

 are the effects of chemical heat-producing processes. The finest 

 parts of the blood are a kind of nervous ether that ascends from 

 the heart to the brain. 5) Baco and Descartes were the first, who 

 considered heat as a mode of motion, and Descartes extended his 

 views also to light, electricity, and magnetism. 



With the observation of Galvani in the year 1780 of the 

 convulsions of a frog's leg brought in contract with two metals, 

 the view of Galvani found numerous followers, and men like 

 Humboldt were among the admirers of the new vital theory. 

 However Volta's experiments an contact-electricity soon eclipsed 

 the results of Galvani, and when the latter succeeded in the 

 year 1793 in adducing irrefutable proof of the presence of an 

 electrical current in the animal : electrical contraction without 

 metals, it did not find grace with the scientific public ; the 

 doubts and distrusts created by Volta were mightier than the 



1) Plato, Phaedon 97, 98. 



2) Aristotle (Editio Bekkeri) de part. anim. II, 1; III. IV, 4, 7 ; V. 2. — Hist, 

 anim. I. XVII. — De respiratione VI. 



3) Plato, Tim. 493 etc. 



4) Democrit, in : Aristotle, de respiratione IV. 



5) Rene Descartes works, edited by H. Kirchmann, II, 27. 



