8 
ESSAY ON SECRETION, 
The oxygen carried to these tissues by the arterial blood 
with which they are supplied, is the active agent in the 
production of those necessary changes, and hence result the 
depression and final loss of both muscular and nervous 
power which follow upon a deprivation of that indispensable 
element. 
I cannot enter fully into this subject, tempting though it 
be; I must therefore content myself with referring you to 
‘ Carpenter’s Manual of Physiology/ in which you will find 
much interesting and valuable information connected there¬ 
with. 
When we consider the continual demand for the develop¬ 
ment both of nervous and muscular force, for the carrying 
on of the unceasing movements of respiration and the cir¬ 
culation of the blood, we shall not be surprised that a very 
considerable quantity of matter has daily to be removed 
from the blood by the various secretory glands, and we shall 
also be able to comprehend the necessity for increased 
activity on their part, w T hich is involved in the performance 
of severe exertion of any kind. 
Further than this, we know that there is a constant 
liability to the introduction into the circulating current of 
materials fit for use in the body, but in excessive quantity, and 
also of materials more or less unfit for use in the organism, 
or even positively injurious thereto. Now, all these sub¬ 
stances are removed by virtue of the excretory function of 
the secreting glands, and the rapidity with w hich they may 
be removed is remarkable. For instance, I find that Mr. 
Erichsen, in one instance, detected ferrocyanide of potassium 
in the urine within one minute after it had been swallowed 
in solution. 
Of course, in this case, all the circumstances concurred in 
favouring the rapid absorption and excretion of the salt, as 
usually a longer period would be required for the occurrence 
of the necessary changes. 
Besides these already enumerated uses of the various 
secretions, I have to mention another, which has been con¬ 
sidered as one belonging to the bile; namely, that of fur¬ 
nishing a quantity of combustible matter, which, being taken 
into the blood, is there converted into carbonic acid and water. 
This was first alleged, I believe, by Liebig; and you will 
find it maintained by Todd and Bowman, in their c Physio¬ 
logical Anatomy/ 
The principal argument in its favour, seems to be the 
small quantity of true biliary matter which is found in the 
faices, more especially of carnivorous animals. 
