DIGESTION. 5Q3 



from the experiments of Eberle, Muller, and Schwann, that cer- 

 tain articles of food, when put into glass tubes containing saliva, 

 and kept at the temperature of 100, are dissolved. This, in par- 

 ticular, is the case with starch, which, by digestion in saliva, is con- 

 verted into gum and sugar. 



The food thus ground down by the teeth and moistened by the 

 saliva, passes along the oesophagus into the stomach, which is a 

 strong membranous and muscular bag, situated in the upper 

 part of the abdomen, immediately below the diaphragm, and ra- 

 ther more inclined to the left than the right side, especially when 

 distended with food. The innermost or villous coat is said to be 

 larger than the other coats, and therefore to be wrinkled into 

 folds ; but this is not very evident on dissection, if we except the 

 fold distinguished by the name of the valve of the pylorus. 



In the stomach the food undergoes a farther change, being 

 converted into a kind of pap, called chyme. The food, after 

 mastication in the mouth, still retains its sensible qualities, and 

 may be recognized by the colour, taste, and smell which it pos- 

 sessed before mastication ; but when food is converted into chyme 

 its sensible qualities are altered. We can no longer recognize 

 the kind of food which has been taken into the mouth. This 

 change of the food into chyme is the first step in the process of 

 digestion a step altogether performed by the stomach. 



It seems to follow from the observations of Dr Wilson Philip 

 that in rabbits, which live entirely on vegetable food, those parts 

 only of the food are changed into chyme which come in contact 

 with the internal coat of the stomach. This organ, in conse- 

 quence of its muscular coat, appears to be in motion, similar to 

 the peristaltic motion of the intestines, during the whole process 

 of ventricular digestion. By this motion those portions of the 

 food which have been converted into chyme are pushed forward 

 towards the pyloric orifice, and new portions of the food come in 

 contact with the stomach to undergo a similar change. 



Frdrn the experiments of Dr Stevens it is evident that in the 

 human stomach food may be converted into chyme without com- 

 ing in contact with its innermost coat* His experiments were 

 made upon a man who supported himself by swallowing stones 

 for money. He had accustomed himself to this practice from 



* See his Thesis De Alimentorum concoctione, printed in Edinburgh in the 

 year 1777. It was inserted in the lirst of the four volumes of theses published 

 in Edinburgh by Elliot in 1786. 



P P 



