THE WORK OF THE DIGESTIVE GLANDS. 



the most part has already appeared in print. But many unpub- 

 lished facts which the laboratory is now in possession of will also be 

 referred to. 



In view of the chief duty which the digestive canal has to perform 

 in the living organism, it may be compared to a chemical factory, 

 where the raw materials the foodstuffs are submitted to an essen- 

 tially chemical process. They are thus brought into a condition in 

 which they are capable of being absorbed into the body fluids and made 

 use of for the maintenance of the processes of life. This factory con- 

 sists of a series of compartments, where the food, according to its 

 properties, is either retained for a time or at once sent on to the 

 next. The factory and, indeed, each single compartment is provided 

 with suitable reagents. These are either prepared in neighbouring 

 little workshops, buiied in the walls of the structure itself, or else in 

 distant and separate organs, which are connected, as in other large 

 chemical factories, with the main laboratory, by a system of trans- 

 mitting tubes. These latter are the so-called secreting glands with 

 their excretory ducts. Each of the workshops furnishes a special 

 fluid, its own particular reagent, endowed with definite chemical 

 properties which only act on certain portions of the food, this latter 

 being ordinarily formed of a complex mixture of different ingredients. 

 These properties are chiefly determined by the presence of special sub- 

 stances in the reagents, the so-called ferments. The separate fluids, 

 the digestive juices, as they are usually termed, attack at one time only 

 a single ingredient of the food, at another several. They thus combine 

 the properties of many individual reagents, each of which acts in its own 

 special way. But even a juice which has only one ferment is a very com- 

 plex fluid, since, in addition to the ferment, it holds other substances 

 also in solution to wit, alkalies, acids, albumin, &c. 



Physiology has learned all this by obtaining either the fluids in 

 question or the pure ferments from the organism, and studying, in the 

 test-tube, their effects upon the constituents of the food as well as their 

 reciprocal behaviour towards each other. Indeed, it is mainly upon 

 knowledge thus acquired that the teaching of the science with regard to 

 the elaboration of the food or, as we say, of digestion, is based. 



But our conception of the digestive process, which is essentially 

 deductive, suffers from many and not unimportant defects. A con- 

 siderable gap without doubt exists between such a form of knowledge 

 on the one hand and the physiological reality, or even the empirical 

 teaching of dietetics, on the other. Many questions still remain unde- 

 cided, many have not even been raised. For example, why are the fluids 

 poured out on the raw material in one particular order and not in any 

 other ? Why are the pi'operties of certain reagents often repeated in 



