206 Chemical Properties of Animal Fluids. [Sei>i. 



Secreted Fluids. 



There exists no problem in chemistry more difficult to solve 

 than that of the secretion of animal fluids. The circulating fluid 

 is carried to the organized laboratory which nature employs, no 

 foreign ingredient is added, no chemical reagent is interposed, 

 and yet the fluid which flows from these organs has acquired 

 chemical properties, which render it decidedly different from 

 the common circulating mass. Not only is the chemical agent 

 which produces these changes unknown to us, but we shall in 

 vain search for any analogous chemical operation. It is doubt- 

 less easy to conjecture, that it is by the influence of the nervous 

 system that this decomposition of blood into the secreted fluids 

 i? effected ; but what is this influence? If electric, how can it 

 be brought to accord with our present knowledge of electric 

 agency? But avoiding vain conjectures on a subject which 

 perhaps will ever remain a mystery, let us determine, from the 

 knowledge we already possess, the chemical nature of the ma- 

 terials of their products. In proportion as we acquire light on 

 the nature of the former, the analysis of the latter becomes 

 more and more interesting, and much may be done by a judi- 

 cious comparison of the one with the other. 



There are two classes of secreted fluids ; namety, the secre- 

 tions, properly so called, or the fluids intended to fulfil some 

 ulterior purpose in the animal economy; and the excretions 

 which are directly discharged from the body. The fluids of the 

 former class are all alkaline ; and of the latter, all acid. The 

 excretions are the urine, the perspired fluid, and the milk. All 

 the other fluids appear to belong to the former class. 



The alkaline secreted fluids may be divided into two very dis- 

 tinct species. The former of these contains the same quantity 

 of water as the blood, so that the change induced by the ner- 

 vous influence seems to be confined to that of altering the che- 

 mical form of the albuminous materials, without affecting their 

 relative proportion to the water and other substances dissolved in 

 the blood. The bile, spermatic fluid, &c. are of this kind. 

 The latter species consists of fluids in which the influence of the 

 nervous system has separated a large portion of the albuminous 

 matter, and left the remaining liquid proportionally more watery. 

 The saliva, the humors of the eye, and the eftused serum of 

 membranes, are of this species; and in these the quantity of salts, 

 and in general also of alkali, is the same as in the blood. 



The influence of the chemical agent of secretion is therefore 

 chiefly spent upon the albuminous materials of the blood, which 

 seems to be the source of every substance that peculiai'ly charac- 

 terizes each secretion, each of which is sui generis, and is its 



