14= PHYSIOLOGY FOR BEGINNERS < HAI-. 



very soluble form, and, moreover, of changing ordinary proteids 

 such as albumin and globulin, which will not diffuse, that is, 

 will not pass through a membrane from a solution rich in 

 them to a solution poor in them, into a form of proteid which 

 will diffuse. The change is effected by the ferment pepsin, 

 which, in the presence of hydrochloric acid, changes all 

 kinds of proteids into a very soluble and a diffusible form 

 of proteid called peptone. Partly on account of these 

 properties, peptone can be more readily absorbed than other 

 proteids. 



Obtain the stomach of a recently -killed pig, cut it open 

 and wash it out. Scrape off the soft inner mucous coat, 

 mince this finely, rub it up with some dilute hydrochloric 

 acid (.2 per cent) and put it in a warm place. After a few 

 hours strain off some of the fluid. This fluid will be very like 

 normal gastric juice and will digest proteids quite well. Into 

 some of it put a few shreds of fibrin or a bit of the white of a 

 hard-boiled egg and set it in the warm. In about an hour you 

 will find the fibrin or egg-albumin will have nearly disappeared. 

 It has been turned into the soluble proteid peptone. 



Rennin is a ferment which causes milk to clot, and it does 

 this by acting on the casein of the milk in such a way as to 

 make the milk set into a jelly, in much the same way as fibrin 

 ferment acts on the fibrinogen of the blood and causes 

 blood to clot. The material called rennet, which is used in 

 the making of cheese, is obtained from the stomach of the calf, 

 and its use depends on the presence of this ferment. 



The Food in the Stomach. When the food, mixed with 

 saliva, and having perhaps a little of its starch turned into 

 sugar by the saliva, reaches the stomach, the flow of gastric 

 juice which takes place soon renders the whole mass acid. 

 This puts an end to any further action of the saliva on the 

 starch, for ptyalin is destroyed by acid. The contractions of 

 the muscular coat of the stomach, first of one part, then of 

 another, move the food about and thoroughly mix it with the 

 gastric juice as this is being secreted ; a kind of churning of the 

 contents of the stomach takes place and the whole is brought 

 to a semi-fluid consistency. During this time the proteids of 

 the food, such as the albumin globulin, myosin, are acted on 

 by the pepsin whether they have been solidified by cooking (a> 



