2 88 SCIENCE PROGRESS. 



This formula is similar to that for the work done in the 

 compression of a gas at constant temperature. We can 

 now apply this to the special case in which the kidney 

 separated from the blood-plasma with A = - 0*56 C, 200 

 c.c. or urine with A = 2*3°. 



In order to produce from 100 ccm. of a fluid with 

 A = -o"56°C, a fluid with A = 2*3°G, the volume of the 

 fluid must be reduced to 24*348 c.c. (0*56 : 24*348 :: 2 '3 : 100). 

 Hence 76*65 c.c. of pure water must be pressed out of every 

 100 c.c. of the original solution. By replacing these figures 

 in the above formula we get : — 



A = 100 x 0-56 (log, roo - log, 24-35). 



= 100 x 0*56 (log 100 - log 24 *3 5) x 2 '302 58. 

 = 79-11. 



In this act of concentration, however, the 76*65 c.c. 

 water which are pressed out enter a medium, not of pure 

 water, but of lymph and blood with A = — o*56°C. The 

 osmotic difference therefore which has to be overcome in 

 the concentration is not represented by 23, but only by 

 2*3 — o*56°C. Hence the work done A will be not 79*1 1, 

 but 79*1 1 - 75*65 x 0*56 = 36*75. 



To reduce this result to gravitation units we must 

 multiply by 122*7 (A = - i°C. corresponds to 122*7 metres 

 water), and thus find that 4509*5 gram metres work are 

 necessary to produce from 100 c.c. fluid with A = - *56°C, 

 24*35 c - c - °f secretion with A = 2*3°C. Hence if the 

 kidney has secreted 200 c.c. of urine with A = — 2*3°C, the 



work it has performed is represented by - x 4*5092 



kilogram metres = 2>7'°37 kilogram metres. 



Dreser then proceeds to investigate the work done in 

 the secretion of concentrated and dilute urines, and also the 

 effect of diuretics on this work. One interesting result he 

 obtains relates to the maximum force of the kidney. From 

 a cat which had been deprived of water for three days he 

 drew off some urine with A = - 4*72°C. The blood at the 

 same time had an osmotic pressure corresponding to 

 A = - o*66°C. These figures denote an osmotic difference 

 of 498 metres water, i.e., a pressure of 49,800 grams per 



