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.^ 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. 1 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) 5 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, g8. 
2) Aristotle (Editio Bekkeri) de part. anim. II, i; 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) René Descartes works, edited by H. Kirchmann , II, 27. 
