The liver has two chief functions,* which are so distinct in their ultimate object that they may be conveniently described separately. One of these, namely, the secretion of bile, is mainly excrementitious.
Bile is one of the fluids connected with digestion, being poured into the intestine, and therefore is treated under this heading; but its influence upon digestion is not so great as was formerly supposed.
Fig. 71. Section of the Liver of the Newt, in which the bile ducts have been injected, and can be seen to fine a network of fine capillaries.
The other function of the liver is nutritive, consisting in the formation of glycogen. The glycogenic function of the liver belongs to the history of the nutrient materials after their absorption, and is of the first importance in attaining the elaboration of the blood, and will therefore be reserved for the chapter on that subject.
* The formation of urea may also be mentioned here, for there is no doubt, as will be seen later on in speaking of the excretions, that the liver has an important share in producing this substance.
Among the most striking peculiarities of the liver may be mentioned the following facts: (i) It has a receptacle, the gall bladder, for storing the secretion until required. (2) It has a double blood supply. It receives by the hepatic artery a small supply of fresh arterial blood as well as all that coming from the spleen, pancreas and intestinal canal, collected by the tributaries of the great portal vein, and distributed by its branches to the liver. (3) A regular network is formed by the minute channels (bile capillaries), which freely anastomose between the cells. (4) Although in the embryo, and in many animals, the liver is a compound saccular gland, the arrangement of the duct radicles and the saccules is so modified in the higher animals and man, that their relationship is no longer apparent, and the structure is best understood by following its vascular groundwork.