REGULATION OF ENVIRONMENT 79 



was not diluted as a whole there was a very slight 

 diminution in the proportion of salts to water. Some 

 of the salts had presumably passed from the blood 

 into the water contained in the intestine, with the 

 result of decreasing very slightly the percentage of 

 salts in the blood. The enormous extra secretion of 

 water was the response of the kidney to this very 

 slight change. At the end of the extra secretion the 

 conductivity had returned to normal. 



When, instead of pure water, a dilute solution of 

 sodium chloride in water was drunk, there was again 

 an enormously increased secretion of urine. This was 

 accompanied by an easily measurable dilution of the 

 blood, and the slightly increased conductivity showed 

 that not only water but also salt was in slight excess 

 over the other constituents. Both water and salt pass 

 out in the urine, though at first very little of the salt 

 goes, indicating that the excretion of the extra water 

 is a process independent of the excretion of the extra 

 salt. 



After prolonged sweating, so as to deprive the body 

 of much water, the urine becomes very scanty and 

 concentrated. But in this case the blood may not 

 become measurably more concentrated, even though 

 the body has lost by sweating a quantity of water 

 nearly equal in weight to the whole of the blood. 



The regulation of the proportion of water in the 

 blood can thus be placed side by side as regards deli- 

 cacy with the regulation of its reaction and compo- 

 nents : its pressures of C0 2 and oxygen, its percentage 

 of sugar, urea, salts, and albuminous substances. Had 



