On Muscular Motion and Animal Spirits 265 



after taking chalybeate drugs a sulphureous and 

 vitriolic odour is perceived in the throat, such as 

 is usually produced from iron corroded by an acid 

 liquid. Further, milk is coagulated in the stomach 

 as it is when an acid liquid is added to it, and food 

 when eaten not unfrequently becomes sour. 



As to these things, I shall in the first place 

 assume that the digestion of food is effected by the 

 animal spirits, brought by means of the nerves, of 

 which there are many inserted in the stomach, and 

 that according as the animal spirits come to the 

 viscera which serve for digestion in greater or in 

 smaller abundance, so the digestion of the food is 

 accomplished more quickly or more slowly. Hence 

 if any one soon after a meal sets himself to study, 

 or thinks much upon a difficult subject, so that the 

 animal spirits are to a great extent detained in the 

 brain on account of strained contemplation and 

 greater agitation of the mind, the function of 

 digestion is not properly performed on account of 

 the deficiency of animal spirits ; but the undigested 

 food remaining in the stomach produces heaviness 

 and discomfort there, as anyone can observe in 

 his own case. Yet, on the other hand, when 

 the mind is free from thought, or even in sleep, the 

 concoction of food goes on at the best ; that is to 

 say, in so far as the animal spirits, not being engaged 

 in carrying on other functions, are abundantly 

 supplied to the viscera devoted to digestion. This is 

 also indicated by the fact that soon after a rather 

 full dinner or supper we usually have an inclination 

 to sleep. For, indeed, when the stomach is replete 

 the animal spirits for the greater part retire to the 

 cerebellum and thence to the lower part of the 

 abdomen to carry out the office of coction, so that 



