6 PHYSIOLOGY AT THE FARM. 



rived from the blood, which is poured into the long tube of the in- 

 testinal canal, far exceeds the amount of the excrement thrown 

 off at the fundament. How this should happen is easily un- 

 derstood, when it is known that absorption goes on freely 

 from living surfaces, so that the humid material, more or less 

 fluid when secreted, is reabsorbed, sometimes after various 

 changes, within the intestinal canal, and restored to the blood, 

 either separately or along with that part of the food which 

 serves for nutriment to the blood. Owing to this absorption 

 of the fluid previously mixed with it, the excrement is for the 

 most part somewhat consistent or even solid. It amounts 

 in general to near a fifth or a sixth part of the food taken 

 in within an equal period of time. Though somewhat solid, it 

 contains as much as three- fourths of its weight of water ; but 

 this is even less than the proportion of water present through- 

 out the bodily frame, which is commonly estimated at four- 

 fifths of its weight. The solid food of animals, though varying 

 much in this respect, generally contains something approach- 

 ing to a like proportion of water. The loss which an animal 

 body sustains in a given time, while its weight remains sta- 

 tionary, is compensated for, not only by the food, but also by 

 the drink taken in within that period. The loss of the liquid 

 part of the living system is by other channels than the bowels 

 namely, by the urine, or the secretion of the kidneys ; by 

 what is carried off from the lungs with the expired air, or the 

 pulmonary exhalation ; by what is thrown off by the skin, or 

 the cutaneous transpiration. To the loss of weight sustained 

 by the living body through the bowels, the kidneys, the lungs, 

 and the skin, must be added the loss, more or less considerable 

 according to circumstances, which the external surface of the 

 body undergoes by friction. The outer surface of the integu- 

 ments, including the hairs, is covered by a peculiar structure 

 known as the cuticle or epidermis, and also called epithelium. 



