SECRETION AND EXCRETION 343 



Other studies seek to explain the nature of the colloid constituents. 

 These may be mucin (MoRNER* 2 ), chondroi tin-sulphuric acid and 

 nucleic acid, which, according to the studies from F. HOFMEISTER'S 

 Institute, do not pass through dialyzing membranes. Moreover, 

 animal gum (LANDWEHR and BAISCH) and a nitrogen-containing 

 complex carbohydrate (SALKOWSKI) probably belong to the urine 

 colloids. That the yellow coloring matter of the urine, urochrome 

 of G. KLEMPERER, is not a colloid has been shown by DETERMEYER 

 and WAGNER * as well as by L. LIGHT WITZ and ROSENBACH.* 



The fact that the surface tension of normal urine is about 10 per 

 cent lower than that of water may also be attributed to certain col- 

 loid constituents (see W. D. DONNAN and F. G. DONNAN* as well as 

 J. AMANN*). 



If we approach the question teleologically, the purpose of the col- 

 loids in normal urine is obviously that the urine be excreted clear. 

 They prevent the formation of sediments within the body. WOLF- 

 GANG PAULI as well as H. BECHHOLD and J. ZIEGLER have shown 

 that the presence of albumin decidedly increases the solubility of 

 uric acid; and J. LICHTWITZ showed that the same property was 

 possessed by the urine colloids. 1 He writes of a case (loc. tit., p. 154) 

 of myelogenous leukemia in a woman : 



"It (the urine) was clear, strongly acid, free from albumin and albumoses. 

 It always had a sediment of well-developed uric acid crystals, etc. The urine was 

 clear only on October 27; the undialyzed urine had no protective action until the 

 urine of October 27 was examined, then the gold figure was about 0.4 c.c." 



Though the protective action of the colloids has been demon- 

 strated only for uric acid, in my opinion it is probably of signifi- 

 cance also for other substances which tend to sediment. 



A normal amount of colloid in the urine is essential; if it is de- 

 ficient it may lead to the formation of urinary calculi, as has been 

 shown by H. SCHADE (see p. 272). 



B. Pathological Urine. 



The kidney behaves like a very sensitive membrane. A slight 

 rise in blood pressure, even venous congestion, suffices to permit the 

 appearance of proteins in the urine. If the kidney has been damaged 

 so as to change the kidney parenchyma, we are not surprised to find 

 constituents of the blood mixed to a greater or less extent with the 

 urine. 



1 As early as 1902, G. KLEMPERER called attention to the action of colloids 

 such as soaps, gelatin and starch paste in interfering with the precipitation of 

 uric acid (G. KLEMPERER, Verh. d. Kongresses f. inn. Medizin, Wiesbaden, 1902). 



