DIURESIS 195 



Simple diffusion through a membrane impermeable to colloids 

 will answer as well. Increase in blood flow instead of pressure 

 regulates the amount of dialysate. Furthermore, it is generally 

 stated that capsular fluid has the same composition as blood, less 

 the colloids. No direct evidence of this has been produced. 

 Theoretically, it is not probable. Colloids have not only the 

 power of holding salts by adsorption, but globulin especially, holds 

 water and sodium chloride in solution. This was proved by 

 Milroy and Donegan, who showed that even when 250 c.c. of water 

 per hour passed the outside of a collodion membrane, a solution 

 of globulin in 0-15 per cent, sodium chloride lost practically no 

 salt in six hours. Any salt over the amount mentioned rapidly 

 passed through the membrane. 



It does not matter whether the filtration or the dialysing function 

 of the capsule is accepted as correct, it is clear that no energy is 

 expended by the kidney in carrying out the process. If filtration 

 occurs, the energy to force the fluid through the filter comes from 

 the heart ; if dialysis be the process, molecular forces are involved. 

 Proof of this lack of work on the part of the capsular cells may be 

 sought in the oxygen consumption of the kidney when it is known 

 that the tubule cells are not particularly active. Such is the case 

 when a diuresis (free flow of urine) is caused by the injection of 

 Ringer's solution. This solution contains the various salts of the 

 blood plasma in their correct proportions, and thus its administra- 

 tion leads to a temporary dilution of the colloids of the plasma. 

 The dilution is merely temporary, because there is an almost 

 immediate increase in the amount of urine secreted, but the increase 

 in the oxygen consumption of the kidney is relatively small (Fig. 47). 



Saline Diuresis. The introduction of the saline fluid has caused : 



(1) A temporary increase in the volume of blood corresponding 

 to the amount of the fluid injected. 



(2) An increase in general blood pressure and therefore an 

 increased pressure in the renal arterioles. 



(3) An increase in the rate of the blood flow through the kidney 

 vessels. Richards and Schmidt showed that ordinarily, blood 

 flows through only a part of the glomerular capillaries, but that 

 saline diuretics cause the closed capillaries to open, and so allow 

 the blood to flow through a greater nuinber. 



(4) A decrease in the concentration of the corpuscles of the 

 blood. This results in a decreased oxygen carrying power and a 

 decreased viscosity. 



(5) A dilution of the colloids of the blood. 



The saline dimrsis may have been caused by all or any of these 

 concomitants. Thev mav be eliminated one bv one. 



13—3 



