Discussion 151 



parenterally. It is said that one of the safeguards in oral ingestion of 

 water is the fact that eHmination goes on about as fast as absorption. 



Talbot : As far as water, sodium and potassium are concerned, it is six 

 one way and half-a-dozen the other whether they are taken by vein or by 

 mouth. With phosphorus, where calcium and other substances may carry 

 it out in the gut, there may be some large differences. 



Bull: I believe there is a speed of infusion beyond which this theory is 

 not correct. If, for instance, very frequent samples of blood are taken 

 during transfusion, when a solution which is not isotonic is being given, 

 very high values may be found. I agree that if the balance studies are 

 taken for 24 hours, the result will be the same. But you can reach values 

 acutely which are well outside what you consider to be the normal range, 

 though fortunately without apparent ill effects. The picture of homeo- 

 stasis varies very markedly with the period over which you are consider- 

 ing it. My colleague Dr. Graber finds that if you go back to the finer detail 

 you may pick up oscillations in values which reveal the mechanism more 

 clearly than do the long-term studies. 



Talbot : Rates of input which are expressed per square metre per day 

 mean are intended to represent the average rate of input throughout the 

 24-hour period. In other words, the fact that one may take as much as 15 

 litres of water per m.^ per day does not mean that one could tolerate this 

 volume if it were given in a fraction of the day. Indeed, were one to give 

 the 15 litres in 12 rather than 24 hours, one would be giving it at the rate 

 of 2 X 15 or 30 litres per m.^ per 24 hours. Such a very high rate of 

 input would produce signs of intoxication only if it were sustained for a 

 sufficient length of time. Thus, 30 litres per m.^ per 24 hours would be 30 

 divided by 24, or 1 -3 litres per m.^ per hour. One would have to infuse 

 water at this rate for at least 70 minutes to produce the 5 per cent gain in 

 body water necessary to induce overt signs of water intoxication. 



Another factor which enters into such consideration is adaptation time. 

 Some of the body's homeostatic mechanisms, such as those concerned with 

 water, potassium and sugar, can adapt quite fully within two or three 

 hours, while others, such as those responsible for phosphorus and sodium 

 homeostasis, may require two or more days. In considering the ceiling 

 and floor levels reported here, an effort was made to take this variable 

 into account and to set forth ceiling and floor levels which the normal 

 individual should be able to attain without becoming seriously disturbed 

 metabolically either during the period of adaptation or later. 



While it may be possible to set up experimental circumstances in which 

 there are differences in the body's tolerance for water and the various 

 electrolytes when given intravenously as compared to orally, for all ordi- 

 nary practical purposes the body's tolerance for these substances is 

 about the same whether they be given by mouth or by vein. 



Fourman : Is it not true to say that with an excessive intake of water 

 the individual will vomit, and with excessive intake of potassium the 

 individual will, extraordinarily promptly, get diarrhoea? 



Talbot : It is true that loss of thirst and nausea constitute accessory 

 mechanisms which serve to protect the organism against the development 

 of water intoxication by the oral route. On the other hand, we have 



