16& ANIMAL PHYSIOLOGY. 



viously pointed out (p. 103) that the biliary acids are decom- 

 posed in the intestine, and that the products are probably 

 in part absorbed. The kind of nourishment resulting from 

 decomposition of the biliary acids, and taken up again from 

 the intestine, is not known, but it may be pretty safely con- 

 jectured to be fatty; in which case, the action of the liver, so 

 far as that material is concerned, would be the preparation 

 of fat from nitrogenous matters. But it is not to be for- 

 gotten that an excessive secretion of bile is a cause of purg- 

 ing, and may thus be altogether got rid of by the bowel. 

 The functions of the liver may therefore be grouped under 

 the three heads of arrest, decomposition, and elimination. 



On the whole, especially when the large size of the liver 

 before birth is considered, and the work thrown on that viscus 

 in the case of Europeans in hot climates, it may be hazarded 

 as a conjecture that, besides being a storehouse for non- 

 nitrogenous material not immediately required, the liver aids 

 the elimination of albuminoids with less complete decompo- 

 sition, and therefore less evolution of heat, than is required 

 to decompose them in the tissues. 



127. The Kidneys. The kidneys are the principal elimi- 

 nators of nitrogenous debris and of salts from the blood. In 

 the human subject they are about four inches long, two and 

 a half broad, and flattened from before backwards. On the 

 inner side of each is a depression called the hilus, where the 

 renal artery enters, and the vein and duct emerge. The 

 duct is called the ureter ; it is dilated at its commencement, 

 but diminishes rapidly to the size of a goose quill, and after 

 a course of fourteen inches or more, opens into the lower 

 part of the urinary bladder. 



The kidney is a tubular gland, and in all classes of verte- 

 brata its tubules present, at or near their origin, small grape- 

 like bodies, called Malpighiaii corpuscles. In many fishes 

 the two kidneys extend the whole length of the abdomen, 

 from the head backwards, and in many they are blended in one 

 mass behind. In the other vertebrata, the permanent kidneys 

 are preceded, in the embryo, by a pair of primordial kidneys 

 or Wolffian bodies, originally extending along the sides of 

 the vertebral column, but afterwards confined to the hinder 

 part of the abdominal cavity. These consist, like the per- 



