THE MECHANISTIC CONCEPTION 5 



preservation of function reduce the blood flow 

 through the kidney, and the secretion of urine 

 ceases; reduce the blood flow through the brain, 

 and the loss of memory is followed quickly by loss 

 of consciousness. Even more obvious than the 

 mechanical features of the circulation are the 

 mechanical principles involved in movement and 

 locomotion. The same systems of levers that have 

 been utilized in machines made by man come into 

 constant use, in highly refined ways, in the animal 

 organism. The application of such principles as 

 these in human locomotion was well understood by 

 Borelli, the Italian physiologist, who more than 

 two hundred years ago published an ingenious essay 

 on the subject ("De Motu Animalium"), in which 

 he set forth the mathematical principles involved. 

 Descartes, in the seventeenth century, was deeply 

 impressed with the idea that the brain is the organ 

 which subserves sensation, thought, and emotion, 

 and that some alteration in the state of the matter 

 of this organ is the regular antecedent of the state of 

 consciousness described by the words " sensation," 

 " thought," and "emotion." His insight extended 

 also to a knowledge that the movements of animals 

 depend on changes in the forms of the muscles and 

 that these changes in form result from processes 

 that go on in the matter of the nerves going to the 

 muscles ; and he further realized that the sensations 

 of animals are dependent on changes in the matter 

 of the nerves that connect the organs of sense with 



