336 COLLOIDS IN BIOLOGY AND MEDICINE 



measured the variations of renal volume in a plethysmograph, he an- 

 alyzed the fluid coming from the renal passages for the same time. 



The kidney perfused with a hypotonic solution is firm and pale, 

 no fluid is expressed with pressure; the cells are so swollen that the 

 lumina of the urinary tubules are almost occluded typical swell- 

 ing. The kidney perfused with hypertonic solution is large and soft, 

 much fluid is expressed by pressure, the cells are shrunken and the 

 tubules patent typical shrinking. (See also R. SIEBECK.) 



In the light of MARTIN H. FISCHER'S theory, the explanation of 

 the concentration of the urine and the tubules becomes simple. 

 We need only recall that the tubules are interwoven with capillaries 

 containing venous blood which reabsorb water. This conception is 

 supported by the experiments of R. GOTTLIEB and R. MAGNUS* as 

 well as of E. H. STARLING,* who found a diminished swelling of 

 the organ when the supply of blood to the kidneys was diminished. 



The greater concentration of the urine is not the only fact requiring 

 an explanation, but also the fact that the relative proportion of the 

 individual crystalloid ingredients is different in the urine than in the 

 blood plasma. [A. R. CUSHNY in his monograph on " The Secretion 

 of Urine," 1917, divides the constituents of the plasma into threshold 

 bodies and nonthreshold bodies. Dextrose, chlorids and sodium are 

 excreted only when their concentration in the blood exceeds a certain 

 definite or threshold percentage. Urea is an instance of a substance 

 with no threshold. According to AMBARD (Presse Medicale, April 25, 

 1918), threshold substances are necessary for cell life. He quotes 

 CHABANIER'S research showing that nonthreshold substances have 

 a common secretory constant for each individual and that they all 

 seem to be solvents for fats. Tr.] 



Though in the blood, 75 per cent of all crystalloids are inorganic 

 molecules according to J. BUGARSZKY and K. TANGL, in the urine they 

 comprise only from 47 to 66 per cent according to J. BUGARSZKY, ROTH 

 and STEYRER. In the blood plasma, 0.58 per cent are NaCl, 0.05 

 per cent urea; in the urine, on the contrary, the average amount of 

 NaCl is 1 per cent in the presence of more than 2 per cent of urea; 

 in the blood there is from 0.08 to 0.12 per cent grape sugar, but only 

 traces occur in the urine. As has been said, it is entirely possible 

 that even during filtration certain changes occur, so that the relative 

 proportion of crystalloids even in the glomerular filtrate differs from 

 that in the blood plasma though the most important change results 

 from the reabsorption of water in the first portion of the tubules. 



That concentration may be brought about by swelling has already 

 been shown in the classical example of C. LUDWIG mentioned on 

 page 66. So much water may be withdrawn from a concentrated 



