100 General Discussion 



potassium is increased in only 20 per cent of our patients. We have 

 noticed that the serum magnesium increases more rapidly and more 

 frequently than serum potassium. During chronic renal failure we 

 have found exactly the same thing. The serum magnesium begins to 

 increase when the urea clearance is below 15 ml./min., even if serum 

 potassium remains normal for a long time. 



McCance: That agrees with observations Miss Watchorn and I 

 made in 1932 (Biochem. J., 26, 54). We generally found that the 

 serum magnesium was high in chronic renal failure and indeed 

 searched for such cases when we wanted high values for our ultra- 

 filtration experiments. 



Scrihner: I want to bring to your attention the work done by Dr. 

 Konrad Buettner, professor in the Division of Climatology at the 

 University of Washington, Seattle (1953. J. appl. Physiol., 6, 229). 

 His observations bear on the sweating data that we have heard 

 and also on considerations of cellular tonicity. If you study water 

 transfer through skin and exclude sweating, the normal human skin 

 will absorb water into the skin against an osmotic gradient that is five 

 times isotonic. In other words if you expose it to increasing concen- 

 trations of sodium chloride solution, the skin will take up water until 

 a concentration which is five times isotonic is reached. The mecha- 

 nism of absorption is not known and there has been no work to 

 elucidate why this occurs. The rate of absorption in an adult human is 

 about 20 ml./hr. for the total skin, and is correspondingly less for 

 smaller areas of skin. Such factors as the storage phenomenon etc. 

 have been excluded by the methods of undertaking this study. The 

 practical implications of this are perhaps of interest. For example, at 

 low rates of sweating, data on electrolytes in sweat may be abnor- 

 mally high throughout due to this absorption, and there is some chance 

 that by the proper control of conditions you may be able to absorb 

 water in survival experiments at sea, since sea water is only three 

 times isotonic. 



Davson: What happens to the water? Is it immediately carried 

 away by the capillaries? 



Scrihner: Yes. Deuterium studies have shown that. Ten — twenty 

 ml./m.^hr. are the actual figures for the absorption. 



Talbot: In the last war in survival ration studies we immersed 

 some very dehydrated volunteer subjects in the equivalent of sea 

 water for an hour or so, and were unable to detect any absorption of 

 water through the skin, using changes in total body weight as an 

 index; so this is very interesting. 



Scrihner: The problem of controlling sweating during these studies 

 is a difficult one and this investigator has gone to great lengths to 

 control this variable. 



