SECRETION 34I 



Also, since p v = RT, 



"RT 

 p = or = cRT. 



v 



Putting these values in the integral, we have 

 A = rcRT 2-3 log ~ - 



c 



In our particular case, w = 0'36, c = (H8, e' = 0'36, and RT = 262'9 kg. metres 

 at 37, so that 



A = 0-36x262-9 (2-3 log g^j - Q ' 36 I. ' 18 )- 18-28 kg. metres. 

 \ U'lo (J'ob / 



We now, in imagination, repeat the operation on this same solution, using a piston 

 which is impermeable to urea, permeable to water and sodium chloride with the 

 other solutes. The compression has to raise c of O'Ol to c' of 0'4 ; n is 0'4, and 

 therefore A is 



= 0-4 x 262-9 (2-3 log ^ - ' 4 ~^' 01 ) = 290 kg. metres. 



The total work is therefore 



18-28 + 290 = 308-28 kg. metres. 



By the simple process of calculation of total concentration by which a glomerular 

 nitrate of initial concentration of 0-18 + 0-01=0-19 molar ( = c) is raised to one 

 of 0-36 + 0-40 = 0-76 (c') by aid of a piston impermeable to urea and sodium 

 chloride, we have, since w = 0'76 



A = 0-76x262-9 (2-3 log ^- '"J?' 19 ) = 127-2 kg. metres. 

 \ U'/b / 



Thus, when we take account of the different partial pressures of urea and sodium 

 chloride, we obtain 2*5 times as great an expenditure of work. 



It may be pointed out that the work calculated in this manner is simply 

 that necessary to effect the change of molar concentrations, and is independent of 

 any particular process by which it is effected. The actual work done by the 

 cells depends on the efficiency, in the engineer's sense, of the machinery by 

 which the energy is afforded. The method can therefore equally well be used 

 to find the osmotic work necessary to secrete a liquid more dilute than blood, 

 as is done by von Rhorer (pp. 383, 384). 



Since the glomerular filtrate has a lower osmotic pressure than the blood plasma by the 

 amount of that of the colloids in the blood, it is clear that some energy is required for the 

 separation in question. This is small, on account of the low osmotic pressure of the colloids, 

 and is afforded by the arterial pressure, that is, by the contraction of the heart muscle. 

 Barcroft and Straub (1910) show that the increased flow of urine brought about by injection of 

 Ringer's solution is not accompanied by increased consumption of oxygen by the kidney, and 

 therefore, presumably, by no increased consumption of energy on the part of the renal cells. 



Alkaline and Acid Secretions. This process may be looked upon, from the 

 point of view of the present section, as the change of concentration of hydroxyl or 

 hydrogen ions of the blood into that of the secretion, or as one of the osmotic 

 partial phenomena, as dealt with above in the case of urine. Von Liebermann 

 (1911, p. 34) points out how, in the case of the alkaline pancreatic juice, diminution 

 of the OH' ion concentration of the blood by intravenous injection of lactic acid 

 causes a reduction in the rate of flow of the secretion under a constant stimulus. 

 This might be explained as due to the greater work necessary to raise the 

 OH' ion concentration in the juice to the same height from a lower level ; but 

 there may, no doubt, be other factors in addition. The mechanism of secretion 

 of acid and alkali will be referred to again later (page 359). 



