122 THE PHILOSOPHY OF BIOLOGY 



irresistibly the extension of mechanical law to the 

 functioning of the human organism, and it is significant 

 that he made this extension without including a single 

 chemical idea, and yet produced a logical hypothesis 

 of life as satisfactory and complete in its day as, for 

 instance, the Weismannian hypothesis of heredity has 

 been in ours. 



His hypothesis of the organism was purely mech- 

 anical. It has been said that his organism was an 

 automaton, like the mechanical Diana of the palace 

 gardens which hid among the rose-bushes when the 

 foot of a prying stranger pressed upon the springs 

 hidden in the ground. Its functions were matters of 

 hydraulics : of heat, and fluids, and valves. His physi- 

 ology was Galenic, apart from Harvey's discovery of 

 the motion of the blood in a circuit, for he did not 

 accept the notion of the heart as a propulsive apparatus. 

 The food of the intestine was absorbed as chyle by the 

 blood and carried to the liver, where it became endued 

 with the ' natural spirits," and then passing to the 

 heart it became charged with the " vital spirits " by 

 virtue of the flame, or innate heat, of the heart, and 

 the action of the lungs. This flame of the heart, fed 

 by the natural spirits, expanded and rarefied the blood, 

 and the expansion of the fluid produced a motion, 

 which, directed by the valves of the heart and great 

 vessels, became the circulation. The more rarefied 

 parts of the blood ascended to the brain, and there, in 

 the ventricles, became the " animal spirits." 



Subtle and rarefied though they were, these animal 

 spirits were a fluid, amenable to all the laws of hydro- 

 dynamics. This was contained in the cerebral ven- 

 tricles, and its flow was regulated just like the water 

 in the pipes and fountains of the garden mechanisms. 

 From the brain it flowed through the nerves, which 



