210 EXCRETION. 



of these may not be actual proximate principles, but sub- 

 stances produced by the processes employed for their extrac- 

 tion, some, which have thus far been discovered only under 

 pathological conditions, may yet be found in health, and 

 they represent, perhaps, important physiological acts. 1 



Fatty Matter. A certain quantity of fat and fatty acids 

 are said to exist in the normal urine. 2 Their proportion, 

 however, is small, and the mere fact of their presence, only, 

 is of physiological interest. 



Inorganic Constituents of the Urine. 



It is by the kidneys that the greatest quantity and variety 

 of inorganic principles are discharged from the organism; 

 and it is probable that even now we are not acquainted with 

 the exact proportion and condition of all the principles of 

 this class contained in the urine. In all the processes of nu- 

 trition, it is found that the inorganic constituents of the blood 

 and tissues accompany the organic matters in their various 

 transformations, though they are themselves unchanged. In 

 fact, the condition of union of the inorganic with the or- 

 ganic principles is so intimate, that they cannot be com- 

 pletely separated without incineration. In view of these 

 facts, it is evident that a certain part, at least, of the inor- 

 ganic salts of the urine is derived from the tissues, of which, 

 in combination with organic matters, they have formed a 

 constituent part. As the kidneys frequently eliminate from 

 the blood foreign matters taken into the system, and are 

 capable sometimes of throwing off an excess of the normal 

 constituents which may be introduced into the circulation, 

 it can be readily understood how a large proportion of some 



1 For further information concerning these principles, the reader is referred 

 to works treating of the pathology as well as the physiology of the urine. A 

 succinct statement of our positive knowledge regarding the doubtful principles 

 is given by Robin (Leyons sur les humeurs, Paris, 1867, p. 688, et seq.). 



2 ROBIN, op. cit. t p. 690. 



