ESSAY ON SECRETION. 
67 
reabsorbed into the blood, if from any cause its passage out 
of the body be checked or prevented; when it produces jaun¬ 
dice, with the mischief attendant thereon. 
Before we can say anything of the circumstances which 
sometimes modify the secreting process, we must first define, 
as well as we are able, the causes by which it is brought 
about, and then we shall be ready to understand its modi¬ 
fications. 
From what has been already stated, it follows, that in order 
to the performance of any act of secretion there must be, 
first, the material to be secreted within the blood; secondly, 
living cells, which by their growth shall remove from the 
blood those parts of that fluid which are to form the secre¬ 
tion ; thirdly, the blood and the secreting cells must be 
brought into connexion the one with the other; and then 
finally, the cells having taken from the blood the elements of 
the secretion, it must be freed either by the rupture or lique¬ 
faction of the cell-walls, or else by exudation through the 
walls, the cells themselves remaining intact. 
We are now come to the last part of our subject, viz.: 
The consideration of some of the circumstances 
which modify the secreting process. —The former 
part of this essay has occupied so great a length as to pre¬ 
vent me doing justice to this division of my subject. Instead, 
therefore, of entering fully into its consideration, I propose 
to submit to you a few facts, and my opinions on them.' 
So far as I can see, the only circumstances by which any 
secreting process can be modified, consist—First, in the 
alteration, either by way of increase or diminution, of the 
quantity of that material in the blood which serves to consti¬ 
tute or make the secretion ; secondly, in its alteration in 
quality, either by addition thereto, or removal therefrom, of 
certain elements; thirdly, in the production of a changed 
condition of the secreting glands or gland-cells; or else, 
fourthly, in the alteration of the supply of blood to the 
gland, and the rapidity of the circulation within it. 
Some of these modifvino* circumstances arise within the 
•/ O 
organism, and result from either healthy or morbid changes 
going on there. Take, for example, the secretions of bile and 
urine, both of which are materially diminished by inaction 
and increased by exercise, in consequence of the production, 
by exertion of the muscular and nervous tissues, of materials 
which constitute these secretions; the nitrogenous parts of 
the disintegrated tissues being more especially carried off' in 
the urinary secretion ; and the hydro-carbonaceous parts in 
that of the liver. 
