390 



contents diluted respectively 10, 20, 40, 80, 160, and 320. With normal 

 juice, a solid clot is obtained with dilutions of 10. 20,40; a dilution of 

 80 gives a cheesy clot, and of 160 a flaky clot. This method is of value 

 for clinical purposes. 



The amount of pepsin present is most quickly and conveniently 

 estimated by the use of carmine-stained fibrin. It is only an 

 approximate method. It depends upon the fact that, as the fibrin 

 becomes digested, the liberated carmine stains the solution. There- 

 fore, the deeper the tint, the greater the amount of the enzyme. The 

 exact amount of carmine set free is gauged by comparison with an 

 artificial scale of solution of carmine of known strength, and thus the 

 activity of the enzyme is estimated. 



Another method consists in the digestion of coagulated egg- 

 albumin in narrow tubes of known dimensions ; it is only accurate for 

 very weak pepsin solutions, since after a certain amount of digestion 

 stagnation ensues. Recently, several accurate methods have been 

 introduced. One depends upon the fact that a suspension of coagu- 

 lated egg- white becomes quite clear under the influence of pepsin. 

 Various quantities (0-2 to 1 c.c.) of the enzyme are added to 5 c.c. of 

 this suspension and 1 c.c. of 0-4 per cent. HC1, and the time at which 

 clearing occurs noted. The egg-white suspension is prepared by 

 rubbing up egg-white in a basin until it is of uniform consistence. 

 This is then slowly mixed and rubbed with water until it is diluted 

 five times. After straining through gauze, the solution is heated at 

 60 C. for twenty minutes, and again strained. For use this is again 

 diluted nine times. 



The description of the anatomy and digestive processes already 

 given above applies to man and the carnivora. In many other animals, 

 the lower end of the oesophagus is dilated to form a crop, or proventri- 

 culus, which functionates as a reservoir. In the horse and pig, this 

 passes into the stomach without any marked constriction; food there- 

 fore passes easily from one part to the other. In ruminants, the crop 

 is modified into a large rumen, or paunch, and a small honeycombed 

 reticulum. The rumen acts as a reservoir for the swallowed food. 

 The function of the reticulum is apparently to hold fluid and moisten 

 the foodstuffs in the rumen preparatory to the " chewing of the cud." 

 From the rumen, the food is returned again to the mouth, the cud is 

 chewed, and again swallowed. This time it is passed through the 

 rumen into the omasum by means of the unfolding of a double fold 

 in the roof of the rumen. The omasum, sometimes termed by butchers 

 " the Bible," is an organ containing many strong muscular leaves. 

 These leaves are covered with coarse epithelium, and the organ, by 

 its movements, churns the food into a proper consistency for entering 

 the rest of the alimentary tract. It yields no digestive secretion. 

 The true stomach, with its digestive fluid, is the next chamber, and 

 is known as the " abomasum." Here digestion proceeds, as already 

 described. 



