66 
ESSAY ON SECRETION. 
because they are removed by the kidneys as fast as formed, 
so long as they retain their normal structure and functions; 
but let their secretory function be suspended, and at once 
there will be an accumulation of these principles in the 
blood. 
The kidneys of dogs have been removed and ligatures 
placed upon the renal arteries, with a view to the solution of 
this question, and in every case urea has been found to 
accumulate in the blood. Further, disease of the kidneys, in 
the human subject, destroying their secretory power, leads 
to the same result; and physicians are able to trace many of 
the symptoms associated with renal affections to the poisonous 
effects produced by this accumulation of urea. These facts 
seem to me to be conclusive as to the pre-existence of the 
materials of the urinary secretion within the circulating fluid, 
and similar facts can be adduced with reference to the secre¬ 
tion from the liver, although the only element of the bile 
which has yet been detected in healthy blood is the choles- 
terine. But the accumulation of the biliarv secretion in the 
m/ 
blood, in cases of suspended activity of the liver, is every 
day to be observed, it being indicated by the tint com¬ 
municated to the various tissues by the colouring matter of 
this secretion. 
Viewing this fact, and in the absence of any reasonable 
ground for the assertion that the gland-cells of the liver 
possess a power denied to those of the kidney, I conclude 
•that the bile pre-exists in the blood, and is but separated 
therefrom by, and not manufactured in, the liver. 
If necessary, I could advance similar arguments with 
reference to all the other secretions; but I think that it 
would only be a waste of your time; and therefore I shall 
simply state that their composition offers no ground for 
objection to this theory, and that we may fairly conclude 
that they are all formed upon one plan—all the materials 
existing in the blood, from whence they are removed by the 
secreting-cells of the glands. 
This conclusion seems to be opposed to the theory of 
Liebig as to the uses of the bile, to which I have before 
adverted; for if it thus exists in the blood, there can be no 
necessity for its reabsorption after it has been removed 
therefrom by the action of the liver. But if this burning up 
during respiration be its principal purpose, why is it secreted 
in such a quantity during foetal life, when respiration is not 
carried on, as is the case ? 
But while thus questioning the accuracy of Liebig’s asser¬ 
tion, it must be admitted that bile is a fluid which is readily 
