9 Dec., 1907.] Elements of Animal Physiology. 763 



young wet clover, the gases produced bv fermentation are excessive, and 

 a dangerous distension of the crop (hoven) may be produced. 



In the horse and pig, the contents of the crop pass readily into the 

 fundus, the two being practically confluent. But in the ruminants, the 

 passage into the fundus is roundabout, and involves a return to the mouth. 

 In the process of rumination (chewing the cud) the contents of the rumen 

 are forced in small poxtions at a time intO' the oesophagus, and by a reverse 

 peristalsis into the mouth. The mass is then subjected to a thorough 

 grinding by the teeth., and is once more swallowed. This time, however, 

 the food mass is not delivered into the rumen by the cesophagus, but by 

 means of a double fold on the roof of the rumen which, closing over, 

 becomes a tube, it passes into the omasum or manyplies. The character- 

 istic feature of this organ is the presence of strong muscular leaves lined 

 with coarse stratified epithelium which, by their movements, rasp the food 

 and if they do not actuallv break up some of the fibres, at least roll thi ■ 

 and work them so that the food mass is fit to enter the remaining portions 

 of the canal. The omasum contains a few glands, but they are of little 

 importance. The reticulum or honeycomb acts as a reservoir of fluid, 

 moistening the food mass which is to be ruminated or passed into the 

 omasum. Its exact significance, however, has not been fullv worked 

 out. There is no true digestive secretion, nor is there any absorption from 

 the proventriculus. 



In the fundus of the true stomach (abomasum of ruminants) we find 

 that the lining membrane is secretorv and capable of pouring out a diges- 

 tive fluid called gastric juice. Gastric juice consists chiefly of water, but 

 it has also some very important ingredients, namely, hydrochloric acid, 

 pepsin and traces of other ferments. The amount of hydrochloric acid 

 varies with different animals, and even in the same animal with different 

 diets ; generally speaking as much acid is secreted as the protein present 

 can absorb, and frequentlv a little more, making the free acid present 

 equal to 0.2 to 0.4 per cent. The uses of hydrochloric acid are : — 



1. To combine with the proteins and so alter them that they can 



be attacked by pepsin ; 



2. To act in the duodenum as an exciter of the pancreas, liver and 



dueodenal glands ; 



3. To act as a bacteria-trap killing many, but by no means all, 



bacteria. 



Pepsin is an enzyme which can transform proteins into proteoses 

 (albumoses and peptones) which latter are much simpler bodies and 

 better able to be absorbed. Pepsin however can only act if the protein 

 be altered by treatment with acid and hence the significance of the hydro- 

 chloric acid. Traces of lipase or fat-splitting enzyme are also found 

 in the gastric juice but the activity of this ferment is very small. Another 

 enzyme frequently described as occurring in the stomach is rennin which 

 clots milk, changing the caseinogen into casein; but it is very probable 

 that this action is produced by the pepsin, in fact it seems to be a property 

 of every enzyme acting on protein. In herbivores and omnivores one 

 always gets lactic acid in the stomach, but this most probably is derived 

 from the carbohydrate of the food b\ fermentative change.^ Salts are 

 also present, the same as are found in the blood, namelv chlorides and 

 phosphates of soda, potash, lime and magnesia. 



