334 COLLOIDS IN BIOLOGY AND MEDICINE 



and, consequently, abstracts water from the intestinal mucous mem- 

 brane, causing absorption from the intestinal lumen. The reverse 

 process occurs in the kidneys. These are traversed by great streams 

 of arterial blood which can give up water. If this assumption is 

 correct, every increase in the supply of oxygen to the kidneys in- 

 creases urine secretion, and every interference decreases it. Now, 

 every elevation of blood pressure and everything favoring the 

 circulation in the kidneys signifies an improvement hi the supply 

 of oxygen and vice versa. We might, however, wherever this occurs, 

 just as well attribute the change in the secretion of urine to the 

 changed filtration pressure or rate of filtration. On this account we 

 must select the circumstances which M. H. FISCHER mentions, which 

 always indicate an improvement or impairment in the supply of 

 oxygen. Among them is, "that blood poor in oxygen or rich in 

 carbonic acid supplied to the kidneys for the briefest period and 

 without even the slightest disturbance of the circulation otherwise, 

 is inadequate to maintain even for the briefest period a normal 

 secretion of urine by the kidneys." On the other hand, there are 

 diuretics which cause an increased secretion of urine though accompa- 

 nied by no change in blood pressure. M. H. FISCHER injected 

 hypertonic solutions of various sodium salts (chlorid, bromid, iodid, 

 sulphate, tartrate, phosphate and citrate) and obtained with them an 

 increased kidney secretion, which stood in a certain relation to the 

 lyotropic action of the salts involved. M. H. FISCHER explains his 

 results by the fact that the salts involved act by shrinking or de- 

 hydrating the body colloids, and thus increasing the quantity of the 

 free or filterable water (see also E. FREY*). Sugars, especially 

 dextose, act similarly. M. H. FISCHER and A. SYKES thus explain 

 the thirst and diuresis of diabetics. 



Some diuretics, for instance, urea, cause no increased circulation 

 of blood, yet they still increase the kidney secretion as J. BARCROPT 

 and BRODIE showed. This has been urged as an argument against 

 the theory, of filtration. In my opinion the explanation is as follows : 

 urea obviously causes deflocculation of the colloids included in the 

 kidney filter. We know from pages 55 and 162 that urea lowers 

 the melting point of gelatin, decreases its rate of solidification and 

 facilitates diffusion through gelatin. All these factors produce a 

 readier filterability of the water of the blood and a greater per- 

 meability of the renal filter; to what extent the reabsorption of 

 water is influenced cannot be decided. 



The experiments of E. LAMY and A. MAYER * seem an additional 

 factor in favor of the filtration theory. They tested the relationship 

 between the viscosity of the blood and diuresis. The following 

 tables definitely show that with the diminution of friction, the 



