500 LECTURE XXI. 



considered in this connection. Digestive activity is especially favored 

 by broths, extracts, juice of meats and milk, and is somewhat stimulated 

 by water and small amounts of alcohol. Fats, on the other hand, restrain 

 the production of the digestive fluid, and also influence its qualitative and 

 quantitative composition. These effects may be observed to best advan- 

 tage by introducing the different substances into the stomach of an 

 animal without its knowledge. The secretion under such conditions does 

 not take place as quickly, usually not until after 15 to 30 minutes, 

 and persists for various lengths of time according to the nature of the 

 food. Experiments of this nature give one the impression that such 

 a direct stimulation of the glands is incomplete in effect. A har- 

 monious course of digestion is only assured when the secretion is strongly 

 stimulated reflexively. We can indeed imagine that by means of 

 digestion itself, substances are formed constantly which act as chemical 

 irritants upon the lining of the stomach and the glands, so that after 

 the flow of the juice is once started, it continues for a considerable 

 length of time. 



Pawlow and his students obtained very interesting results when they 

 attempted to ascertain the effect of different kinds of food. It was found 

 that the cells of the stomach did not produce the same juice in all cases. 

 On the contrary, the composition of the digestive juice was suited to the 

 nature of the food. First of all, it is of interest to know that the acidity 

 of the juice remains constant in the secretion, while the amount of ferment 

 present varies greatly. Now it is a well-known clinical fact that widely 

 divergent degrees of acidity are found in the contents of the stomach. 

 Such determinations, however, are of but a slight value, for many reasons; 

 on no account should they be used to indicate the amount of hydrochloric 

 acid normally present in the gastric juice. As we have already men- 

 tioned, it is not right to regard the contents of the stomach as a uniform 

 mixture of the digestive secretion and the food. As Griitzner * has recently 

 proved, the newly-introduced food stands in the midst of that which has 

 been in the stomach for some time, and does not at once come in contact 

 with the walls of the stomach. In the ' pars-splenica of the stomach, the 

 food may remain for hours without coming into intimate contact with the 

 gastric juice. If now a part of such a digesting mixture be siphoned out 

 of the stomach, it is obvious that a determination of the degree of its acidity 

 might easily give rise to false conclusions. Quite a number of factors 

 here come into play which may easily conceal the fact of the original 

 uniformity in the acid content of the juices. It has been observed, 

 for example, that with dogs in which there was a vigorous secretion, there 

 was more acid in the gastric juice than when the production of the same 

 took place more slowly. Similarly a higher acidity was noted if the juice 



' Pfliiger's Arch. 106, 463 (1905). 



