370 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



as the true gastric secretion ; but, since these substances are always mixed 

 in actual digestion, they -will answer for the study of the process of diges- 

 tion, even although they will prevent accurate statements as to the 

 chemical constitution of this secretion. The gastric juice in the horse 

 is secreted onlj- by the glands of the fundus from a surface about two 

 hand-breadths in extent. Extracts from this portion of the mucous mem- 

 brane contain more acid, more ferments, and, what is remarkable, more 

 mucin than extracts made from the pyloric portion. Ellenberger and 

 Hofmeister found that the degree of acidity immediately after eating was, 

 in the horse, only 0.084 per cent. After an hour the acidity rose to 

 0.1 per cent., and still later to 0.2 per cent. Immediately after eating 

 no hydrochloric acid was present, but only appeared four or five hours 

 after the commencement of the meal. Lactic acid was always present, 

 apparently even in excess of hydrochloric acid. This maj', perhaps, serve 

 to explain the fact that in the horse's stomach the change of starch into 

 sugar may go on even in the presence of 0.2 per cent, of acid, as organic 

 acids interfere less than mineral acids with this process. The charac- 

 teristics of the acid of the gastric juice have been found to depend upon 

 the food. Thus, these authors have found that the distribution of acids 

 was as follows :— 



Hydrochloric Acid. Organic Acids. 



1. Oats and ohopped straw, . . 0.163 per cent. 0.287 per cent. 



2. Oats, ....... 0.490 " 0.610 



3. Hay 0.022 " 1.798 



It is thus seen that when the food consists of oats the maximum 

 percentage of hydrochloric acid is found in the gastric juice, while when 

 hay is given the mineral acid falls to a minimum, while the organic acids 

 are in excess. The importance of these facts is evident when it is remem- 

 bered that oats contain 12 per cent, of albuminous matter and 65 per 

 cent, of carbohydrates, including cellulose, while hay contains only 9 per 

 cent, of proteids and 70 per cent, of carbohydrates. Hence, when oats 

 are given, the excess of hydrochloric acid is especially favorable for the 

 peptonization of the proteid constituents, while it interferes with the 

 digestion of the carbohydrates. On the other hand, when hay is given, 

 the excess of organic acids, as already mentioned, does not interfere with 

 the action of ptyalin on starch, while still permitting the peptonization 

 of the proteids. 



The watery extract of the mucous membrane of the fundus differs, 

 as already mentioned, from that of the pylorus. It contains more mucus, 

 more acid, and more ferment. The fundus extract contains a ferment 

 which converts casein, fibrin, albumen, and gelatin into peptone in media 

 containing 0.15 to 0.5 per cent, of hydrochloric acid. While 0.6 per 

 cent, of hydrochloric acid arrests digestion, in the case of organic acids 



