THE MALPIGHIAN BODIES OF THE KIDNEY. 
77 
of the vascular system, and other circumstances. Hence the kidneys appear to share 
in the office of regulating the amount of water in the body. How admirably the 
structure of the Malpighian bodies fits them for thus acting as a self-adjusting valve 
or sluice to the circulation, I need not explain. 
It may possibly be considered by some, that, in the preceding observations on the 
use of the aqueous element of the urine, and on the nature of secretion in general, I 
have been endeavouring to illustrate a doubtful hypothesis by speculations more 
doubtful still, obscurum per obscurius. But I rest my view of the function of the 
Malpighian bodies principally on anatomical grounds, and the other considerations 
have been introduced in connection with it, rather in consequence of the interest 
they appear to me to add to it, than because I am fully satisfied of their validity. 
Undoubtedly both questions are worthy of being separately handled, and require a 
much wider and more elaborate investigation than seems yet to have been given 
them. Meanwhile they may in turn receive some elucidation from the researches 
detailed in this paper. Parallel lines of inquiry into the anatomical varieties of the 
Malpighian bodies and uriniferous tubes, and into the chemistry of their secretion, in 
the different tribes of animals and in various stages of their development, could 
scarcely fail either to confirm or to confute what has now been advanced. 
I shall conclude with three remarks founded on the foregoing facts and speculations. 
1. The bile and the urine have been ever classed together as the most important 
excretions. The former is secreted from venous blood ; the latter it has been thought 
from arterial blood, except in some inferior animals, in which the blood from the 
lower part of the body circulates through the kidneys. But it is a most striking fact, 
that the proximate principles of the urine, like those of the bile, are secreted in all 
animals from blood which has already passed through one system of capillaries, 
in a word, from portal blood ; although it does not appear to what extent its qualities 
are changed by traversing the Malpighian system. The analogy is at least remark- 
able, and may throw some light on the mysterious meaning of the portal circulation. 
2. Diuretic medicines appear to act specially on the Malpighian bodies ; and va- 
rious foreign substances, particularly salts, which, when introduced into the blood, 
pass off by the urine with great freedom, exude in all probability through this bare 
system of capillaries. The structure of the Malpighian bodies indicates this, and 
also, as far as they are known, the laws regulating the transmission of fluids through 
organized tissues, modified in their affinities by vitality. 
3. The escape, also, of certain morbid products, occasionally found in the urine, 
seems to be from the Malpighian tufts. I allude especially to sugar, albumen, and 
the red particles of the blood : the two first of which would transude, while the last 
would escape only by rupture of the vessels*. 
* See Note, p. 67. 
3 Norfolk Street, Strand, 
February 14 th, 1842. 
