ESSAY ON SECRETION. 
13 
we know of the secretion of the testes ; while that of the 
mammary glands contains, in addition to the casein, which 
we may fairly consider as modified albumen, and some saline 
matters, both fat and sugar. So far, then, as the chemical 
composition of these secretions is concerned, we can readily 
imagine that they may exist in the blood, and that the only 
function of the glands consists in the separation of their 
several constituents from that fluid ; but in the bile we have 
a fluid of a more complex character. 
Taking the simplest view of it, as sanctioned by chemists, we 
find it stated to be a combination of an organic acid with 
soda; this organic acid differing in a marked degree from any 
of the constituent parts of the body, and also containing a very 
large amount of carbon, hydrogen and oxygen, with a small 
quantity of nitrogen and a trace of sulphur. In addition to 
this we have colouring matter, and, according to many 
chemists, a peculiar fatty matter, which is called cholesterine. 
The organic acid readily changes into a resinous compound; 
and some analysts have therefore given biliary resin held in 
solution by an alkali as the principal organic constituent of 
the bile, and asserted that all its nitrogen and sulphur were 
contained in albuminous matter which was mixed with this 
biliary resin. 
You will see from this statement that it is not yet very 
certain what are the real constituents of this fluid; but all 
chemists agree in averring that it contains a very large amount 
of hydro-carbonaceous matter, which has been partially 
oxidised. 
In the urine, on the other hand, nitrogenized compounds 
are present in great quantities, and it seems to have a more 
definite composition. 
Its chief organic constituent is urea; a substance con¬ 
taining two equivalents of carbon, two of oxygen, two of 
nitrogen, and four of hydrogen; it having, consequently, a 
greater proportion of nitrogen than any other substance 
within the body. 
There is also contained in the urine an organic acid, which 
in the carnivora is an acid containing, like urea, a large quan¬ 
tity of nitrogen, and called uric acid: but in the herbivora 
we have an acid containing less nitrogen, designated the 
hippuric. Beside these, the organic constituents of urine, 
we meet with a quantity of saline matters, which vary both 
in quantity and in composition under certain conditional 
circumstances. The most constant salts are those of lime, 
soda, and potass. Colouring matter and extractive matter 
are also found, but no definite account is given concerning 
either of these constituents. 
