ESSAY ON SECRETION. 
5 
respect from those which we regard as secreting processes, 
it is better to be considered alone than in connection with 
them. 
Our definition excludes also the formation of adipose tissue 
and of epidermis, from the list of secreting processes, 
although there are many points of correspondence between 
them; and the correspondence is deserving of careful con¬ 
sideration, as it will be found to throw no small light upon 
the general nature of secreting processes. In the article on 
Secretion, in the ( Cyclopaedia of Anatomy and Physiology/ 
you will find arguments adduced for considering fat, hair, 
and epidermis as the result of secretion, but as I have not 
time for quoting them, I must refer you to that work for 
further information on this head. 
You will likewise see that the same views are advanced by 
Mr. Paget, in his lectures reported in the f London Medical 
Gazette/ for 1847, entitled, “ Lectures on Growth, Nutrition, 
and Hypertrophy. 5 ’ 
Accepting, however, as sufficient for our present purpose, 
the definition which I have just given you, we firstly have to 
consider the purposes to which the secreting process is 
rendered subservient; the reasons, in fact, why there should 
be any such thing as secreting organs and secretions therein 
formed. 
These purposes are very various; but I think that we 
may fairly arrange them into four classes : First , and least in 
importance, we have a class of secretions w 7 hich have merely 
mechanical uses, as the lachrymal fluid, synovia, and mucus. 
With these also we must place the secretion of serous mem¬ 
branes, if we consider them as secreting organs; but it 
seems to me that what has been called the secretion of 
those membranes is merely an exudation of a small quantity 
of watery material from the blood, and hardly w r orthy the 
name of a secretion. 
In fact, w 7 e find that the greater number of serous surfaces, 
during life, are only moistened by a little vapour, those mem¬ 
branes having no true fluid in their sacs; the arachnoid form¬ 
ing the only exception to this rule. 
These secretions are all of very simple constitution. 
Thus, tears contain only a little chloride of sodium, with a 
small quantity of animal extractive matter, which in all pro¬ 
bability is derived from the Meibomian glands, besides 
water. Mucus contains an animal matter which has been 
called mucin , which seems to resemble albumen, with a little 
saline matter, principally the lactates and chlorides. Sy¬ 
novia contains six per cent, of albumen, with a little 
