266 DIGESTION. 



the intestines or in the absorbent vessels. That they are much 

 changed appears from the impossibility of detecting them in 

 the blood ; and that part of this change is effected in the liver 

 is probable from an experiment of Magendie, who found that 

 when he injected bile into the portal vein a dog was unharmed, 

 but was killed when he injected the bile into one of the sys- 

 temic vessels. 



The secretion of bile, as already observed, is only one of the 

 purposes fulfilled by the liver. Another very important func- 

 tion appears to be that of so acting upon certain constituents 

 of the blood passing through it, as to render some of them 

 capable of assimilation with blood generally, and to prepare 

 others for being duly eliminated in the process of respiration. 

 From the labors of M. Bernard, to whom we owe most of what 

 we know on this subject, it appears that the low form of albu- 

 minous matter, or albuminose, conveyed from the alimentary 

 canal by the blood of the portal vein, requires to be submitted 

 to the influence of the liver before it can be assimilated by the 

 blood ; for if such albuminous matter is injected into the jugu- 

 lar vein, it speedily appears in the urine ; but if introduced 

 into the portal vein, and thus allowed to traverse the liver, it 

 is no longer ejected as a foreign substance, but is probably 

 incorporated with the albuminous part of the blood. 



An important influence seems also to be exerted by the liver 

 upon the saccharine matters derived from the alimentary canal. 

 The chief purpose of the saccharine and amylaceous princi- 

 ples of food is, probably, in relation to respiration and the 

 production of animal heat ; but in order that they may fulfil 

 this, their main office, it seems to be essential that they should 

 undergo some intermediate change, which is effected in the 

 liver, and which consists in their conversion into a peculiar 

 form of saccharine matter, very similar to glucose, or diabetic 

 sugar. That such influence is exerted by . the liver seems 

 proved by the fact that when cane sugar is injected into the 

 jugular vein it is speedily thrown out of the system, and ap- 

 pears in the urine ; but when injected into the portal vein, and 

 thus enabled to traverse the liver, it ceases to be excreted at 

 the kidneys ; and, what is still uiore to the point, a very large 

 quantity of glucose may be injected into the venous system 

 without any trace of it appearing in the urine. So that it may 

 be concluded, that the saccharine principles of the food un- 

 dergo, in their passage through the liver, some transformation 

 necessary to the subsequent purpose they have to fulfil in rela- 

 tion to the respiratory process, and without which, such pur- 

 pose probably could not be properly accomplished, and the 



