344 C HEM ICO- PHYSIOLOGICAL CONSIDERATIONS ON 
organs, &c. After having established these leading principles of 
physiological chemistry, this celebrated chemist continues thus : — 
“ Under what form does this azote make its escape through the 
urinary passages'? Under the form of ammonia. And here comes 
one of those observations which never fail to fill us with admira- 
tion at the beautiful simplicity of Nature’s operations. 
“ If, in the general course of things, we return to the atmosphere 
the azote which certain vegetables are able at once to make use of, 
we might expect also to furnish the air with ammonia, a pro- 
duct so necessary to the existence and development of most 
vegetables. 
“ Such is the principal result of the urinary secretion ; viz., 
the emission of ammonia, which returns either to the soil or to 
the air. 
“ Ought we not, however, here to remark that the urinary organs 
will become altered in their functions and vitality by the contact of 
ammonia, the same as they will by carbonate of ammonia? — and so 
Nature causes urea to be an excretion as well of man as of animals. 
"UREA is carbonate of ammonia*; that is to say, carbonic acid 
like unto that expired from the lungs, and to the ammonia so grateful 
to plants. But this carbonate of ammonia has been robbed of 
oxygen and hydrogen, ingredients essential to the formation of the 
molecules of water. 
“ Deprived of water, carbonate of ammonia becomes urea ; in 
that state it is neuter, inactive against animal membrane: — in that 
state it may traverse the kidneys, the ureters, the bladder, without 
inflaming them. Once, however, in contact with air, veritable 
fermentation commences in it, which restores to it these two watery 
molecules, converting this urea into true carbonate of ammonia, 
volatile and incapable of exhalation into air ; soluble, capable of 
being taken up by the rain, and so destined to pass from earth to 
air and from air to earth, until the time shall arrive when, imbibed 
by the roots of some plant and elaborated by it, it becomes con- 
verted afresh into organic matter, and serves as food to the 
herbivora, &c.t” 
What is demonstrative of these chemical theories, or rather let 
us say, these novel truths, is that the quantity of urea excreted 
through the urinary apparatus is great in proportion as the regimen 
of the animal contains the mere azote. So that carnivorous and 
omnivorous animals constantly eject with their urine a large 
quantity of urea, which, through fermentation in the air, develops 
* According to Wohler, it likewise represents cyanate of ammonia , which 
is the product of the oxydation of cyanogene and oxyde of ammonium or 
liquid ammonia. 
f Chemical Statistic of Organized Beings, p. 37 and following. 
