586 LECTURE XXV. 



We have repeatedly learned that other glands are to a certain extent 

 independent of the blood-supply. Thus the pancreas is constantly forming 

 its secretion, but gives it up only after certain kinds of stimulation. It is 

 otherwise with the kidneys. Their activity is different, because their func- 

 tion has an entirely different significance from that of all the other glands. 

 The kidneys must be very delicately adjusted to the composition of the 

 blood. They are obliged to work very rapidly in all cases, and are not 

 obliged in every case to follow stimulations which are communicated 

 to them reflexively by the nervous system. The chemical nature of the 

 blood invariably has an influence. Now, is this because the vasomotor 

 nerves are directly influenced by the composition of the blood, so that, for 

 example, an enlargement of the vessel or restriction of it will be effected, 

 or because certain components of the urine act directly upon the epithelium 

 of the uriniferous tubes? We hold that the last assumption is very prob- 

 able, and imagine that certain specific substances are captured by this 

 epithelium, which are concentrated and then given up again. Only in 

 some such way as this are we able to account for the relatively high con- 

 centration of the urea. There are quite a number of different observations, 

 which indicate such a specific function of the kidney epithelium. A few 

 examples will be cited. The elimination of uric acid has been studied 

 most closely, and its presence is easy to detect. 1 If, for example, a solu- 

 tion of uric acid in piperazine is injected subcutaneously into rabbits, 

 there takes place first of all a considerable diuresis. In from twenty 

 minutes to an hour uric acid may be detected in the tubes of the med- 

 ulla. The glomeruli and Bowman's capsules are perfectly free from 

 deposits of uric acid; but, on the other hand, the epithelium of the con- 

 voluted tubes contains granules of uric acid, and chiefly in the end of the 

 tubes facing the lumen. Anten 2 obtained corresponding results in the 

 kidneys of dogs. He cut out the kidneys from the general circulation of 

 a live dog, and then passed a solution of freshly-precipitated silver chloride 

 in ammonia through the organs, in order to precipitate the uric acid present 

 as silver urate. The kernels of the silver salt were found chiefly in the 

 cells of the convoluted tubes, and particularly at the basal part of the 

 cells. The epithelium of the ascending tube of Henle's loop also showed 

 isolated accumulations, but this was not the case with the descending part 

 of the loop. One might naturally be inclined to object that the appear- 

 ance noted might result from a reabsorption just as well as from a secre- 

 tion of the uric acid. There are, however, so many observations 3 of 



1 Cf. Sauer: Arch, mikros. Anat. 53, 218 (1899). W. Ebstein and A. Nicolaier: Ex- 

 perimentelle Erzeugung von Harnsteinen, Wiesbaden, 1891, and Virchow's Arch. 143, 

 337 (1896). O. Minkowski: Arch, exper. Path. Pharm. 41, 375 and 410 (1898). 



2 Henri Anten: Arch, internat. de pharmacodynamie et de therapie, 8, 455 (1901). 



3 Cf. Courmont et Andre": J. physiol. et pathol. general, 7, 255 (1905). 



