50 
MECHANICAL AND IMMECHANICAL PARTS 
cannot tell) is shown by the consequence of the separation 
being long suspended; which consequence is disease and 
death. Akin to secretion, if not the same thing, is assim¬ 
ilation, by which one and the same blood is converted into 
bone, muscular flesh, nerves, membranes, tendons; things 
as different as the wood and iron, canvass and cordage, of 
which a ship with its furniture is composed. We have no 
operation of art wherewith exactly to compare all this, for no 
other reason perhaps than that all operations of art are ex¬ 
ceeded by it. No chemical election, no chemical analysis 
or resolution of a substance into its constituent parts, no me¬ 
chanical sifting or divison, that we are acquainted with, in 
perfection or variety, come up to animal secretion. Never¬ 
theless, the apparatus and process are obscure; not to say 
absolutely concealed from our inquiries. In a few, and only 
a few instances, we can discern a little of the constitution 
of a gland. In the kidneys of large animals, we can trace 
the emulgent artery dividing itself into an infinite number 
of branches; their extremities everywhere communicating 
with little round bodies, in the substance of which bodies 
the secret of the machinery seems to reside, for there the 
change is made. We can discern pipes laid from these 
round bodies towards the pelvis, which is a basin within 
the solid of the kidney. (PI. VI. fig. 2.) We can discern 
these pipes joining and collecting together into larger pipes; 
and when so collected, ending in innumerable papillae, 
through which the secreted fluid is continually oozing into 
its receptacle. This is all we know of the mechanism of 
a gland, even in the case in which it seems most capable 
of being investigated. Yet to pronounce that we know 
nothing of animal secretion, or nothing satisfactorily, and 
with that concise remark to dismiss the article from our 
argument, would be to dispose of the subject very hastily 
and very irrationally. For the purpose which we want, that 
of evincing intention, we know a great deal. And what we 
know is this. We see the blood carried by a pipe, conduit, 
or duct, to the gland. We see an organized apparatus, be 
its construction or action what it may, which we call that 
gland. We see the blood, or part of the blood, after it 
has passed through and undergone the action of the gland, 
coming from it by an emulgent vein or artery, i. e. by an¬ 
other pipe or conduit. And we see also at the same time 
a new and specific fluid issuing from the same gland by its 
excretory duct, i. e. by a third pipe or conduit; which new 
fluid is in some cases discharged out of the body, in more 
cases retained within it, and there executing some impor- 
