DIGESTION OF FOOD. 341 



that, while there is a certain amount of force in the various 

 views stated briefly above, they do not go to the root of the 

 matter. 



Vomiting is a very complex act, implying numerous muscu- 

 lar and nervous co-ordinations. In the natural wild state the 

 horse can have but rare necessity to vomit (unlike the carnivora), 

 hence these co-ordinations have not been organized by habit 

 and use ; they are foreign to the nature of the animal. After 

 rupture of the stomach in the horse, and in sea-sickness in man, 

 the nervous system is profoundly afiFected and the unusual hap- 

 pens ; in other words, the necessary musculai" and nervous 

 co-ordinations take place. At all events, we are satisfied that it 

 lies with the nervous system chiefly. ' 



Similarly, the habit of regurgitating the food is intelligible 

 in the light of evolution. The fact that mammals are descended 

 from lower forms in which unstriped muscle-cells go to form 

 organs that have a rhythmically contractile function, renders 

 it clear why this function may become, as in ruminants, spe- 

 cialized in certain parts of the digestive tract ; why carnivora 

 should vomit readily, and why human subjects should learn to 

 regurgitate food. There is, so to speak, a latent inherited ca- 

 pacity which may be developed into actual function. Apaxt 

 from this it is difllcult to understand such cases at all. 



The vomiting center is usually located in the medulla, and 

 is represented as working in concert with the respiratory center. 

 But when we consider that there is usually an increased flow 

 of saliva and other phenomena involving additional central 

 nervous influence, we see reason to believe in co-ordinated 

 action implying the use of parts of the central nervous system 

 not so closely connected anatomically as the respiratory and 

 vomiting centers are assumed to be. 



THE REMOVAL OF DIGESTED PRODUCTS FROM THE 

 ALIMEKTART CANAL. 



The glands of the stomach are simply secretive, and all ab- 

 sorption from this organ is either by blood-vessels directly or 

 by lymphatics ; at least, such is the ordinary view of the subject 

 — whether it is not too narrow a one remains to be seen. 



It is important to remember that the intestinal mucous 

 membrane is supplied not only with secreting glands but lym- 

 phatic tissue, in the form of the solitary and agminated glands 



