THE FUNCTIONS OF THE DIGESTIVE ORGANS. 495 



liter of air is perceptible. We shall repeatedly come back to the influence 

 of the sensatory impressions upon the functions of the digestive glands. 

 The nerves of smell and of taste are important protective organs. They 

 call attention to processes of decomposition, to decay in our food, and allow 

 us to recognize the presence of many injurious substances. 



From the mouth, the food is carried by the process of swallowing into 

 the oesophagus, and from here directly into the stomach through the cardia. 

 With the exception of a slight transformation of starch into sugar, the 

 real process of digestion does not begin until the food reaches the stomach, 

 where it proceeds energetically. We repeat that the diastase from the 

 saliva can under certain conditions continue its action for some time, but, 

 on the other hand, the stomach itself has its own ferments. As has been 

 recently shown, it possesses, for one thing, a lipolytic ferment, although we 

 have at present no means of estimating the extent of its activity. Its sig- 

 nificance has been quite variously estimated and, in fact, its very presence 

 has been doubted by some. Besides lipase, there are ferments present in 

 the stomach which are capable of acting upon the protein of the foods. 

 These are pepsin and rennin. We have already stated that the existence 

 of the latter ferment has been quite recently questioned, and it has been 

 assumed that the two properties of coagulating milk and dissolving albu- 

 min are due to the action of a single ferment. We can adopt this assump- 

 tion that the action of rennin corresponds to that of pepsin, only when 

 it has been verified by further investigation. Until this has been done, 

 we will content ourselves with the older conception of the presence of both 

 pepsin and rennin, although, we have already seen, there are a number of 

 facts which speak in favor of Pawlow's hypothesis. 



These ferments are produced by certain glands in the mucous membrane 

 of the stomach. The stomach itself is not a physiological unit. Even 

 the outer appearance shows a marked difference between the pyloric and 

 fundus (or cardiac) portions of the mucous membrane. That of the 

 former is pale and has a few deep folds, while the latter is of a reddish- 

 yellow or reddish-gray color, and has numerous folds which are connected 

 with one another by a sort of network. In these net-like little hollows 

 between the folds end the stomach glands. There are two types of these 

 glands, one of which contains but a single kind of cell, while the other 

 contains two. In the pyloric end there is found but one cell form, while 

 in the cardiac or fundus end the glands are of the latter type. There is 

 no sharp distinction between them, however. These two types of glands, 

 both of which are tubular in shape, are named according to the locality 

 in which they are found, and are known respectively as pyloric and cardiac 

 or fundus glands. The former contain a cylindrical epithelium, and the 

 latter contain, in addition, other smaller cells irregularly distributed 

 between the larger cells and the basement membrane. The first kind of 



