XIII. THE ANIMAL 275 



the food is kneaded and incorporated with the gastric juice, the pulpy 

 mass produced being known as chyme. The chyme then passes into 

 the intestines. The proteids are the principal constituents of the food 

 affected by the gastric juice, though the melting of the fat and the 

 removal of the cell walls from fatty tissue are important physical 

 changes. In the case of animals fed upon starchy foods, a slight 

 amount of hydrolysis, resulting in the formation of sugar and also of 

 lactic acid, is said to occur in the stomach. The chief effect, however, 

 may be said to be the action on the proteids. 



The secretion of the glands of the intestines has a strong alkaline 

 reaction and thus tends to neutralise the acidity of the chyme. It has 

 also the property of inverting cane sugar and maltose. The secretions 

 of the pancreas and the liver are next brought into contact with the 

 chyme. 



Pancreatic juice is a viscid liquid of alkaline reaction containing 

 albumin, fat, soaps, alkaline carbonates, phosphates, lime, magnesia 

 and iron. Its characteristic constituents, however, are three enzymes 

 a diastatic one, a lipolytic or fat-splitting one, and a proteolytic one. 



The composition of pancreatic juice appears to be very variable ; 

 the amount of total solids, for example, has been observed to vary 

 from 1'5 to 11*5 per cent. 



Hammarsten states that the solid matter in the pancreatic juice 

 of the horse varies from 0'9 to 1'8 per cent, in that of the sheep from 

 1'4 to 3-7 per cent, and in that of the rabbit from 1-1 to 2-6 per cent, 

 whilst in that of man it is about 2 '4 per cent. 



The amount of ash, chiefly common salt, appears to be generally 

 from 0-6 to 0-8 per cent. 



The most important constituents are, of course, the enzymes. 



(1) The pancreatic diastase or amylopsin. This body is similar in 

 many respects to ptyalin, but appears to be distinct from it. It acts 

 upon starch more energetically, even attacking and dissolving un- 

 boiled starch. It yields dextrin and maltose. 



(2) The fat- splitting enzyme, steapsin, OY pialyn. This enzyme has 

 the power of hydrolysing the fats (i.e., decomposing them into glycerol 

 and free fatty acids, which, in the alkaline liquid, probably form soaps), 

 and at the same time, of emulsifying them. 



The hydrolytic process only affects a very small amount of the 

 fats ; but the emulsification extends to nearly the whole quantity pre- 

 sent, the soaps formed in the first process greatly facilitating the 

 formation of the emulsion. 



(3) The proteolytic enzyme, trypsin. This acts, like pepsin, in 

 digesting proteids ; it differs from the ferment of the gastric juice, 

 however, in acting best in an alkaline solution, and in being more 

 rapid in its action, especially towards fibrin and elastin. In the 

 pancreas itself, little or no trypsin exists, but a zymogen known as 

 trypsinogen occurs. This body, by the action of acids, water, alcohol, 

 or of an enzyme, enterokinase, contained in intestinal juice, splits off 

 trypsin. 



There is some evidence of the existence of a milk-curdling ferment 

 in the pancreatic juice. 



