SECTION VIII 



EXCRETION OF MATTER FROM THE BODY 



1. EXCRETION BY THE LUNGS (see Respiration, p. 294) 



2. EXCRETION BY THE KIDNEYS 



URINE 



THE water and waste nitrogen of the body are chiefly elimi- 

 nated in the urine, which is secreted by the kidneys. 



The tests for the various constituents of the urine must be 

 studied practically. (Chemical Physiology.) 



I. Physical Characters 



The characters of the urine depend largely On the relative 

 proportion of water and of solids which are excreted in it : 

 at one time it may be very concentrated, while at another 

 time it may be very dilute indeed. For this reason its specific 

 gravity, which depends upon the percentage of solids in 

 solution, varies within wide limits. But the average specific 

 gravity in the horse is about 1036. It is possible from the 

 specific gravity to form a rough idea of the amount of solids 

 present, for by multiplying the last two figures by 2*22 the 

 amount of solids per 1000 parts is given. 



Since the percentage of pigments in the urine varies like 

 that of the other constituents, the colour of the urine shows 

 wide divergence in the normal condition. A concentrated 

 urine has a dark amber colour, while a dilute urine may in 

 some animals be almost colourless. Under average con- 

 ditions the urine has a straw-yellow colour. 



The reaction of urine is normally acid in dog and other 

 carnivora. 



