120 THE DOG IN HEALTH. 



salts, and certain nitrogenous compounds, of which the 

 principal is urea. While these are the compounds best 

 known, there can be little doubt that there are others ex- 

 pelled in small quantity, but which, when retained, soon 

 poison and derange the whole mechanism of life a state- 

 ment which applies with more or less force to every body 

 that enters into the excretions. The principal excretory or 

 eliminative organs are the lungs, skin, kidneys, and bowels. 

 Water and carbon dioxide pass off chiefly by the lungs ; 

 nitrogenous waste by the kidneys in the urine. Exactly 

 what is expelled by the bowels beyond the undigested re- 

 mains of food is not so well known. The skin gets rid of 

 a good deal of water, some salts, a little nitrogenous waste 

 (urea), and several acids i. e., in those animals whose 

 skins are very active, as is the case with man and the 

 horse. 



The dog gets rid of an excess of water by the respira- 

 tory tract and the mouth. He does not sweat largely. It 

 would seem as though the kidneys, lungs, and mucous 

 membrane of the mouth of the dog, perhaps also his sali- 

 vary glands, did some of the work that in certain animals 

 is accomplished by the skin. 



The connection between the different excretory organs 

 is important in all animals. Each is supplemental to the 

 other ; each can to a certain extent act for the other, but 

 only for a limited period if the animal is not to suffer. 

 What Nature seems to aim at is a balance of work with 

 division of labor, each organ being a sort of specialist, but 

 one that is not wholly out of touch with the others. 



In all management of animals, in health and in disease, 

 there is no more important truth to be kept in mind than 



