442 PHYSIOLOGY CHAP. 



the water that filters through the glomeruli. Obviously, however, 

 the opposite interpretation may also be sustained, i.e. that the 

 one kidney can only eliminate the salt to a less extent than the 

 normal, so that it is more slowly excreted and in a more dilute 

 concentration. 



Bradford also found that on performing a still more radical 

 renal operation in which only one - sixth of the total bulk 

 of the two kidneys was left in a dog, polyuria properly so called 

 set in, i.e. the excretion both of water and of urea was increased. 

 This more active excretion of urea must be referred to the general 

 conditions which lead to an increased production of urea. The 

 animal, in fact, becomes rapidly emaciated, and soon perishes from 

 marasmus. This result indicates that normal general metabolism 

 depends on the normal functioning of the kidneys. But we are 

 still ignorant of the nature of the process by which renal insuffi- 

 ciency affects metabolism so as to accelerate the katabolic 

 processes. We can only say that, according to some authorities, 

 the kidneys, like many other glands, are the seat of a specific 

 internal secretion which regulates metabolism, and which is quite 

 distinct from the supposed internal secretion (absorption) of water 

 ascribed by some to the convoluted tubules, in explanation of the 

 phenomenon of the formation of urine. 



Many other workers have sought to distinguish the function of 

 the glomeruli from that of the uriniferous tubules. Lindemann 

 (1901) tried to eliminate the glomeruli by means of the vascular 

 circulation. He took advantage of the fact (see p. 424) that the 

 tubules are supplied not only by the blood from the capillaries of 

 the efferent glomerular arteries, but also directly by the blood 

 from the arteriae rectae, so that the whole of the blood circulat- 

 ing in the kidney does not pass through the glomerular vessels. 

 Blood, therefore, still circulates through the kidney, though three 

 times as slowly as under normal conditions, after eliminating the 

 glomeruli, which makes it possible for the tubules to function 

 independently of the latter. In order to exclude the glomeruli, he 

 injected oil directly into the renal artery, on which (as can be 

 seen under the microscope) the glomeruli, exclusively, are cut off 

 from the circulation, because the oily globules penetrate into the 

 rete mirabile. He found that a kidney thus partially embolised is 

 capable of functioning. It is able to pick up and excrete indigo- 

 carmine from the blood as well as a normal kidney, and also 

 secretes an urine, which, owing to the increase in its organic and 

 inorganic products, is more concentrated than the normal. Hence 

 the kidney thus altered is also capable of excreting the normal 

 constituents of urine. On the strength of these experiments 

 Lindemann came to the conclusion that the uriniferous tubules 

 are able to a certain extent to function independent of the 

 glomeruli, so that the excretion of water is not exclusively the 



