718 ADEQUACY OF BLOOD PRESSURE 



secreted. If the glomerular filtrate is practically isotonic with 

 the plasma, then the observed result could be brought about 

 only by the absorption of solids out of all proportion to water. 

 But it may be doubted whether the approximation of the osmotic 

 pressure of the urine to that of the blood during diuresis is 

 really a point in favour of Lud wig's view, as Starling thinks. In 

 hydrsemic plethora it is the clear duty of the kidney to get rid 

 of the excess of water in the blood, and if it does the A of the 

 urine must fall. If the A of the urine in diuresis always approxi- 

 mated closely to that of the blood, it might be considered a point 

 in favour of Ludwig, as showing that the urine always closely 

 resembles the glomerular filtrate, which according to Ludwig' s 

 view must have a definite A in relation to the blood. But 

 Dreser's observations show that in some cases of diuresis this is 

 not the case ; consequently Starling's observations lose to a con- 

 siderable extent the significance which he attributed to them. 

 Galeotti has followed in detail the changes in the quantity and 

 composition of urine and in the work of the kidney, which follow 

 the production of hydrsemic plethora. After injecting hypertonic 

 solutions of sodium chloride or dextrose into dogs, he found that 

 the osmotic pressure of the blood rose immediately, and that the 

 kidney at once started to correct this and the hydraemic plethora 

 with the least possible work to itself. At first the kidney passes 

 out very large quantities of a fluid which is nearly isotonic with 

 the blood plasma and contains large quantities of the injected 

 molecules. In this way the maximal amount of water and of 

 the substance injected are eliminated with the least possible work 

 to the kidney. This urine, which has a A only just greater than 

 that of the blood, is presumably in the main the glomerular filtrate. 

 At the end of two hours the osmotic pressure of the blood has 

 been greatly reduced and at the same time the diuresis begins to 

 pass off. For, it would be clearly impossible for the body to go 

 on parting with the quantities of water necessary for the pro- 

 duction of this nearly isotonic urine, unless it received fresh 

 supplies, because the kidney is secreting not only the injected 

 substance, but also the normal organic solids at the usual rate. 

 Consequently, the diuresis begins to pass off, the molecular con- 

 centration of the urine steadily rises, and with it the work done 

 by the kidney. Galeotti found that after injecting 150 c.c. of 

 10 per cent, sodium chloride solution into an unwatered dog, the 



