THE MALPIGHIAN BODIES OF THE KIDNEY. 
69 
laries by innumerable avenues. But towards the Malpig'hian bodies, there is no 
opening from this capillary network at all corresponding in magnitude or freedom to 
that on the side of the veins. In fact, the only points by which it can discharge 
itself are the efferent vessels of the Malpighian bodies, which are comparatively few 
in number, only capillary in size, and quite disconnected with one another, except 
through the plexus itself. Add to this, that the Malpighian tuft to which they lead 
is a great obstacle to the passage of fluid, from the tortuosity of its minute vessels, 
and by their all having but one point to discharge themselves of the blood they 
already contain, viz. their afferent vessel. Thus to fluid driven through the kidney 
in a retrograde course, there is not only the general impediment offered by the 
aggregate capacity of the arteries being greatly inferior to that of the veins, but a 
vascular arrangement equivalent to a double valve. The capillaries of the tubes form 
a first great cul-de-sac, those of the Malpighian tufts a second, for these may both 
be described as great reservoirs, easily entered from the side of the arteries, but dis- 
charging themselves with great difficulty back again, or towards the arterial tree. 
If it be now considered that the network of the tubes, or the former and far the 
greater of these reservoirs, almost always retains much blood after death, and that 
the Malpighian reservoir is never without a considerable quantity, it will not be 
difficult to comprehend, why injection thrown into the veins reaches not to the Mal- 
pighian bodies, however well it may seem to load the capillaries of the tubes; for 
all the blood must first pass through the difficult channels that have been spoken of, 
and this it never can do completely. I suppose that this view of the subject, which 
is nothing more than a statement of facts, will be deemed a sufficient explanation, 
and that it will not be regarded as necessary to imagine the existence of real valves 
in any part of the course of these small blood-vessels. I have never met with any 
appearance that could lend credibility to such a supposition, which, if true, would 
present an unique structure in the vascular system. Extravasation from the veins 
will sometimes reach the tubes, in consequence of a structure which will presently 
be explained. 
By the Tubes, the Malpighian bodies cannot he injected, nor, without extravasation, 
either the plexus surrounding the tubes, or the veins. 
Many anatomists have taken extreme pains to inject the tubes from the pelvis of 
the kidney, by means of the air-pump, but never has a single Malpighian body been 
thus filled. This, it has been said, is a conclusive proof that the Malpighian bodies 
are not placed at the extremities of the tubes. But I think that if the real structure 
and relation of these parts be duly considered, this constant result will be allowed to 
be in the strictest accordance with the account I have delivered, and even a necessary 
effect of the anatomical disposition of the parts. To those who are acquainted with 
the practical difficulties of the injection of the ducts of glands in general, and espe- 
cially of those which are very tortuous, the following considerations on this subject 
