of Edinburgh, Session 1877 - 78 . 649 
kidney performs its function, and also say a word or two in connec- 
tion with the structure of that organ. As regards its histology the 
kidney may he said to he composed of two elements — (1) the blood- 
vessels. and (2) the tubuli uriniferi. (This is leaving out of account 
the lymphatic arrangement.) The kidney receives its supply of 
blood from the renal artery, which, as it passes into the substance 
of the kidney, penetrates the cortical portion and gives off 
branches. The uriniferous tubules, in this part of the kidney 
end in globular dilatations called the capsules, or Malpighian 
bodies ; it is into these that the branches of the renal artery 
pass to form convoluted coils, the glomeruli. The branches 
of the renal artery which pass into the glomeruli are called the 
afferent vessels, and the vessels that are formed by the reunion of 
the branches of the glomeruli are called the efferent vessels. After 
the efferent vessels emerge from the capsule of the Malpighian body 
they again subdivide to form true capillaries, most of which go to 
form a closely meshed network round the tubuli uriniferi. They 
finally unite to form the radicals of the renal vein. 
To make use of the description of Mr Bowman, “ it would be dif- 
ficult 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 up into 
an assemblage of vessels of far greater aggregate capacity than itself, 
and from which there is one narrow exit. Hence must arise a very 
abrupt retardation to the velocity of the current of blood.” But 
besides this arrangement, by which a large volume of blood is 
exposed to circumstances the most conducive to free filtration of its 
fluid constituents, we have a condition, namely, the secondary capil- 
lary system on the distal side of the glomerulus, which, by its resist- 
ance to the onward flow of the blood, subjects the blood inside the 
Malpighian body to considerable pressure. It is now generally sup- 
posed that the excretion of urine takes place by filtration of a dilute 
solution of the soluble constituents of the urine through the glome- 
rulus into the capsule of the Malpighian body. This weak solution 
then passes along the tubuli uriniferi, where it comes into close con- 
tact with the blood it has just left. It is then supposed that an inter- 
change takes place between the blood in the capillaries surrounding 
