THE MALPIGHIAN BODIES OF THE KIDNEY. 
75 
of the secretion from the secerning - tubules of the gland, is therefore here placed in a 
clear light. 
If this view of the share taken by the water be correct, we must suppose that fluid 
to be separated either at every point of the secreting surface, along with the proxi- 
mate principles, as has hitherto been imagined, or else in such a situation that it may 
at once freely irrigate the whole extent of the secerning membrane. Analogy lends 
no countenance to the former supposition, while to the latter, the singular position, 
and all the details of the structure of the Malpighian bodies, give strong credibility. 
It would indeed be difficult to conceive a disposition of parts more calculated to 
favour the escape of water from the blood, than that of the Malpighian body. A 
large artery breaks up in a very direct manner into a number of minute branches, 
each of which suddenly opens into an assemblage of vessels of far greater aggregate 
capacity than itself, and from which there is but one narrow exit. Hence must arise 
a very abrupt retardation in the velocity of the current of blood. The vessels in 
which this delay occurs are uncovered by any structure. They lie bare in a cell from 
which there is but one outlet, the orifice of the tube. This orifice is encircled by 
cilia, in active motion, directing a current towards the tube. These exquisite organs 
must not only serve to carry forward the fluid already in the cell, and in which the 
vascular tuft is bathed, but must tend to remove pressure from the free surface of 
the vessels, and so to encourage the escape of their more fluid contents. Why is so 
wonderful an apparatus placed at the extremity of each uriniferous tube, if not to 
furnish water, to aid in the separation and solution of the urinous products from the 
epithelium of the tube? 
Many recently discovered facts* conspire to prove that secretion is a function very 
nearly allied to ordinary growth and nutrition ; that whereas growth and nutrition 
comprehend two functions, assimilation of new particles and rejection of old, the old 
being reconveyed into the blood, so secretion consists in a corresponding assimilation 
and rejection, and only differs in the old particles being at once thrown off from the 
system, without re-entering the blood. According to this view, all effete material 
received into the blood from the old substance of the various organs, must be reassi- 
milated by an organized tissue, specially designed for the purpose, before it can be 
* Purkinje, Report of the Meeting of Naturalists at Prague in 1837, Isis, No. 7, 1838. Schwann, Froriep’s 
Notiz. Feb. 1838. Henle, Muller’s Archiv. 1838-9. [See also Cyclop, of Anatomy, Art. Mucous membrane , 
the conclusion of which is only just published, although that part of it relating to this theory was written in 
December last. Mr. Goodsir, since this paper was read, has ably advocated this theory in a communication 
made to the Royal Society of Edinburgh on the 30th of March, an abstract of which I have just seen in the 
London and Edinburgh Monthly Journal of Medical Science, May 1842. In the same publication is a report 
of a paper by the same excellent anatomist, on the structure of the kidney, read at the Med. Chir. Soc. of 
Edinb. on April the 6th. He describes “a fibro-cellular framework, pervading every part of the gland” — 
analogous to the capsule of Glisson, and “ forming small chambers in the cortical portion, in each of which a 
single ultimate coil or loop of the uriniferous ducts is lodged.” This framework is the structure which I have 
described (pp. 70-1) as the matrix. The convoluted tubes and vessels are all imbedded in it . — June 1, 1842.] 
