118 PHYSIOLOGY CHAP. 



fundus, thus excluding the objection that the digestive action of 

 the pyloric juice is due to the presence in the pyloric mucosa of 

 some of the glands which predominate in the mucous coat of 

 the fundus. 



(c) It was formerly held that milk coagulates, on coming 

 into contact with gastric mucous membrane or its extract, 

 owing to the gastric juice, because on merely acidifying fresh 

 milk its casein comes down in a flocky precipitate. But after 

 the experiments of Selmi and Heinz, and the exhaustive work 

 published by Hammarsten in 1872, and confirmed by A. Schmidt, 

 it was recognised that the extract of gastric mucous membrane is 

 able to clot milk even in a neutral or alkaline medium. This 

 phenomenon is therefore independent of acid and is due to a 

 special enzyme, distinct from the pepsin, which is called chymosin 

 (or renniri). 



Hammarsten succeeded in separating the chymosin from the 

 pepsin by neutral lead acetate, which precipitates pepsin but not 

 chymosin. Of unknown chemical constitution, chymosin has all 

 the properties common to other digestive enzymes. In neutral 

 solutions it is destroyed at 70 C., in acid solutions at 65 C. It is 

 not diffusible ; its maximal activity is reached at 38-40 C. Its 

 action is exerted exclusively on the caseinogen of milk, and differs 

 from that of acids, as we shall see in the chapter on Digestion. 

 According to Hammarsten, one part of chymosin is able to clot 

 400,000-800,000 parts of casein. 



Chymosin is present in large quantities in the stomach of 

 sucking animals, especially calves, lambs, and kids. Schumberg 

 found it in 15 out of 34 stomachs of adult men, and in 4 out of 6 

 of new-born infants. It is probably decomposed by the alkalinity 

 of the intestinal juice, or absorbed like other ferments, since it does 

 not occur in the faeces. It seems to originate like pepsin from the 

 pyloric glands and the chief cells of the glands of the fundus. 



(d) The existence of a lipolytic enzyme in the stomach had 

 long been suspected (Cash, 1880 ; Ogata, 1881, etc.). Others, 

 however (Contejean, 1894; Boldireff, 1904), denied the value of 

 previous researches, carried out for the most part in vitro and with 

 artificial extracts of mucous membrane, or with gastric juice 

 extracted by the sound, and attributed the results described 

 either to the adulteration of the substances or to the presence of 

 pancreatic juice that had flowed back into the stomach. Finally, 

 Volhard (1900-1902) demonstrated in a series of experiments that 

 a very active lipolytic enzyme is produced in the stomach, 

 which acts particularly on emulsified fats. This enzyme is 

 contained chiefly in the mucosa of the fundus (in man) or of the 

 pyloric region (dog, cat, pig). Its action is reduced in the presence 

 of acids, and may be altogether inhibited ; this does not, however, 

 occur during the physiological digestion of fat, since the secretion 



