200 THE BODY AT WORK 



supplied with arterial, the tubules with venous, blood. The 

 glomeruli receive branches from the renal artery, the tubules 

 from a portal system derived from veins of the abdomen and 

 hind-legs. 



Sir William Bowman, who in 1842 gave the first detailed 

 description of the microscopic structure of the kidney, con- 

 cluded that, whereas " the tubes and their plexus of capillaries 

 are probably the parts concerned in the secretion of that 

 portion of the urine to which its characteristic properties are 

 due (the urea, lithic acid, etc.), the Malpighian bodies [i.e., the 

 glomeruli] may be an apparatus destined to separate from the 

 blood the watery portion." 



All physiologists are in accord in regarding the glomeruli as 

 the principal seat of exudation. There is great diversity of 

 view as to the function of the tubules. In 1844 Ludwig 

 advanced the opinion that all the constituents of the urine 

 pass through the glomeruli in a large excess of water, and 

 that in the course of the tubules this excess of water is re- 

 absorbed. This theory was based, among other considerations, 

 upon the extreme thinness of the epithelium which covers the 

 glomerular tufts ; he judged that water would filter through 

 it very readily. A large amount of experimental work has 

 been directed to the solution of these two problems viz., 

 (1) Do urea and other similar substances pass through the 

 glomeruli ? (2) Is water returned from the tubules to the 

 venous system ? Our views as to the functions of the kidney 

 as a whole will not be greatly influenced by the answers that 

 may eventually be given to these questions ; yet their discussion 

 is of very great interest, owing to the nature of the evidence 

 which may be marshalled on either side. 



There is, perhaps, no other organ in the body the problems 

 with regard to which seem to be so nearly plain questions of 

 hydrostatics. It is easy to make a model of a urinary tubule 

 and its blood-supply. If such a model were shown to a sanitary 

 engineer, and he were asked to explain the working of the 

 drainage system of the body, and especially to answer the two 

 questions which we have propounded, he would say that there 

 could be no doubt as to the part of it through which most water 

 enters the tube, the glomerulus. He could give no opinion 

 as to whether urea, uric acid, and other substances of a like 



