258 PHYSIOLOGY AT THE FARM. 



the minute vessels enter the Malpighian corpuscles, or little 

 red bodies imbedded in the cortical substance. Their ordi- 

 nary diameter is 1-1 20th of an inch. They are vascular tufts 

 formed by an afferent and an efferent vessel. The afferent 

 vessel divides into from five to eight branches which cover 

 the surface of the corpuscle, and end into a finer set of central 

 vessels. From these last the efferent vessel arises, and, passing 

 out of the tuft, divides into capillaries which form a plexus 

 around the adjacent tubuli. 



The connection between the Malpighian body and the urini- 

 ferous system of tubes is, that th% Malpighian body projects 

 into a blind dilated portion of a tubule, and so obtains a capsule 

 which is pierced both by the afferent and the efferent blood- 

 vessel ; which last, after ramifying on the tubule, terminates in 

 a radicle of the renal vein. 



The following short passage from Professor Bennett's work 

 probably indicates the mode in which the urine is formed : 

 " The two kidneys contain in their cortical substance globular 

 convolutions of capillary vessels which hang in the blind ex- 

 tremities of the tubular glands. This arrangement permits 

 the ready passage of a large amount of water from the blood, 

 which, as it flows out through the duct, receives the secretion 

 formed by the cells which line them." 



The urine of man and that of mammals in general is charac- 

 terised by the large proportion of water which, as compared 

 with its solid constituents, it presents. The solid constituents 

 seldom amount to so much as five parts in a hundred parts of 

 fluid urine. There is, however, no constant relation between 

 the amount of watery flufd and the proportion of solid con- 

 stituents. The kidney, in short, may be described as having 

 two separate functions one being to throw off water when 

 that accumulates in undue proportion in the blood ; the other 

 being to eliminate the saline matters and the peculiar organic 

 products that result from the waste of the tissues. Water 



