594 LECTURE XXV. 



been acidified. Now urea is a good solvent for uric acid. It is an open 

 question whether we are justified in assuming with Rudel l that there is a 

 chemical combination between the urea and the uric acid in this case, 

 and it is equally uncertain whether the urea alone affects the solubility of 

 the uric acid, or whether there are other compounds present in urine which 

 have the same action. 



We have already said that the epithelia of the blood-vessels and of the 

 uriniferous tubes can only cause the elimination of those substances which 

 do not belong to the plasma, or which are present in more than the normal 

 amount. Thus the kidneys, for example, are very sensitive to an increase 

 in the sugar-content of the blood. Albumin does not pass through the 

 kidneys when they are acting normally, except when albumins foreign 

 to the body evade the alimentary canal, and get into the circulation. 

 It is a well-known fact that under pathological conditions, in diseases of 

 the kidneys, albumin passes from the blood-capillaries, and enters through 

 the epithelium of the uriniferous tubes. The presence of albumin in the 

 urine is a symptom which may arise from a number of different processes. 

 There is no question that a study of the nature of the eliminated albumin 

 could be used as a basis for further inquiry. To be sure, in many cases 

 there is a mere appearance of serum-albumin, but we can well imagine 

 that in other cases the tissue-cells for some reason or another produce an 

 albumin, and give it up to the plasma, of a nature which in its entire con- 

 struction is foreign to the plasma, and that it is accordingly eliminated by 

 the kidneys. This is not the place to discuss at any length such questions, 

 which are closely related to the pathology of metabolism. 



As we have already mentioned, the organism can under certain condi- 

 tions eliminate the constituents of the urine through other glands, especially 

 through the skin. Thus in many cases of uraemia, urea may be secreted 

 in such quantities by the sweat-glands, that crystals deposit upon the skin. 

 By uraemia we understand a very serious complex of symptoms, occurring 

 when the kidneys to a greater or less extent have ceased to exercise their 

 functions. The organism seeks by every means in its power to get rid of 

 the constituents of urine which are circulating in the blood. If it does 

 not succeed in accomplishing this, symptoms appear which are similar to 

 intoxication. The attempt has often been made to trace the cause of the 

 disease to some constituent of the urine, and in this connection urea has 

 been principally considered. On the other hand, there are quite a number 

 of observations which indicate that the urine itself exerts a poisonous action. 

 Thus if human urine is injected into the veins of a rabbit, it will produce 

 acute poisoning, which will result in the death of the animal. The urine 

 from different animals shows different degrees of poisonous properties. 



1 Arch.exper. Path. Pharm. 30, 469 (1892). Cf.T. J. Zerner: Wiener klin. Wochschr. 

 6, No. 15, p. 272 (1893). A. Ritter: Z. Biol. 35, 155 (1897). 



