THE MALPIGHIAN BODIES OF THE KIDNEY. 
71 
vessels open by being united to their outer coat, whence results the dark colour, 
usually attributed to congestion, which these cones commonly present, as compared 
with the cortical part, where this matrix is less abundant. This is the structural 
condition which seems to me most easily to explain the remarkable facility with which 
injection, urged along the tubes, enters the veins. The smallest rupture of the matrix 
will crack across the minute vessels accompanying the tubes, and expose their open 
extremities to the entrance of the injection. If the force employed be very moderate 
and equable, extravasation does not occur, and the tubes alone are injected, often to 
the surface, but undue or ill regulated pressure almost inevitably occasions it. Having 
once entered a small vein, through however small an opening, it soon diffuses itself 
through the veins, and the capillaries surrounding the tubes, rather than along the 
tubes, for the reasons above stated ; and, if the organ be then cut to pieces and ex- 
amined, these vessels seem filled, without extravasation ; the tubes are also more or 
less filled with the same colour; and the two structures are so intricately interlaced, 
as to wear the aspect, especially if dried, of one continuous network. The point of 
extravasation escapes observation, and hence the fallacy of imagining a continuity 
between the veins or their capillaries, and the tubes. 
Some distinguished anatomists have held that the tubes end in a plexiform manner, 
and have stated themselves to have unequivocally seen this arrangement in injected 
specimens. I am induced to believe this opinion to be founded on deceptive appear- 
ances ; either such as that above mentioned, or that occasioned by the overlapping 
of injected tubes. Others have considered the tubes to terminate in free blind ex- 
tremities unconnected with the Malpighian bodies, and have likewise rested their 
opinion on the appearances of injected specimens, as well as on those of recent ones. 
As the injection always stops short of the real extremities of the tubes (the Malpighian 
bodies), it must necessarily show apparent free extremities — and others may be pro- 
duced by the section requisite for the examination of the part. As for the false ap- 
pearances presented by recent specimens, they are obviously referable to the sudden 
bending down of a tube behind the part turned to the observer. In a mass composed 
of convolutions, many such must continually occur; and their real nature may be 
easily determined by the use of a high power and varying focus. Other anatomists, 
aware of this last fallacy, and failing to find either a free inosculation of the tubes in 
the form of a plexus, or a termination of them in the Malpighian bodies, have rested 
in the conclusion that the curves of the convoluted part are the looped junctions of 
different tubes. It is obvious that this conclusion is a deduction drawn from the ap- 
parent absence of any other mode of termination, and must be relinquished now 
that the tubes are shown to end in the Malpighian bodies. 
The foregoing account has been drawn principally from my observations on the 
kidneys of Mammalia, but it is intended to embrace the chief points in the anatomy 
of the Malpighian bodies in all the Vertebrate tribes. In all these, I have ascertained 
