304 DIGESTION. 



tions, is contained in the body of an adult. This mass of fluid, 

 which contains only 310 grammes of solid constituents (and there- 

 fore, 3'1) is especially designed to rinse and purify the absorbed 

 food ; and hence we may take the view, long since adopted by 

 Berzelius, that digestion is a true process of rinsing. But how- 

 ever obvious the aim of this abundant secretion of aqueous fluid 

 may be, since it not only favours the solution of the food, but 

 essentially contributes towards its resorption, we ought not to 

 forget that it at the same time imparts an extraordinary motion to 

 the fluid masses within the animal body. The blood within the 

 vessels not only circulates in the course of a few minutes through 

 the whole of the body, but it also carries a considerable mass of 

 fluid into the intestinal canal, from whence, in a longer or shorter 

 time, it is again almost entirely restored to the vessels. This 

 continuous ebb and flow of aqueous solutions can scarcely fail to 

 exert an influence or to react upon the processes of nutrition and 

 metamorphosis generally, which originate in the blood. We might 

 perhaps have formed some idea of these relations from what we 

 learnt of the destiny of the bile in the organism after its secretion, 

 and of the purposes which the formation and secretion of bile were 

 designed to fulfil in the intermediate metamorphosis of matter. 

 We have seen that the bile is poured into the intestine in order 

 to be again almost completely resorbed ; and we have found that 

 not only its water repeatedly circulated through the portal vein, 

 liver, and intestine, but also that its solid constituents were for the 

 most part returned into the blood through the lymphatics. A 

 portion of the organic matters must, therefore, first pass through 

 the stage of biliary formation, and then return from the intestine 

 into the blood, in order that it may be applied to further pur- 

 poses. As the bile shows itself to be not merely a simple 

 secretion, designed for the digestion of definite substances, so also 

 the other secretions, which are poured in such abundance into the 

 intestine without leaving a trace of their solid or fluid constituents 

 in the excrements, may serve to carry away with them from the 

 blood into the intestine different substances which have become 

 temporarily effete, in order that they may be carried back to the 

 blood after having been subjected to metamorphosis, and rendered 

 available for further purposes. 



This transfusion of certain substances into the secretions, and 

 their return into the blood, is not limited to the normal organic 

 and inorganic constituents of the secretions ; for we find, after the 

 copious transfusion of water into the blood, that not only is the 



