38 THE NEW PHYSIOLOGY. 



blood provide the stimuli which regulate the varying 

 activity of the respiratory centre, and we never doubted 

 that similar alterations would be found to account for 

 the varying activity of the kidneys, so we sat down 

 to find them. Using another method of attack, my 

 colleague, Dr Priestley, was able to demonstrate that 

 the electric conductivity of the blood was sensibly and 

 regularly, though only very slightly, diminished during 

 the period of increased secretion. It is known that when 

 water is taken into the intestine, not only is water 

 absorbed, but, for a time at least, salts pass out from 

 the blood into the water. Thus one can probably 

 account for a slight deficiency of salts, or " wateriness," 

 in the blood, without any necessary increases in its 

 volume. This deficiency of salts is indicated by the 

 electrical conductivity method, and doubtless produces 

 the stimulus which excites the kidney to increased 

 action. 



The conception of the kidney to which modern in- 

 vestigation points is thus that of an organ which responds 

 with almost incredible delicacy to various slight changes 

 in the composition of the blood, and so responds as to 

 keep the blood composition normal. The old gross 

 mechanistic conceptions of fifty years ago with regard 

 to the action of the kidneys are entirely obsolete, though 

 they still occupy a time-honoured place in current 

 text-books. The kidney, if it be a mechanism, is, like 

 the respiratory centre, one of extraordinary delicacy 

 and constancy in action, and we are again up against 

 the question how, with such a labile structure as proto- 

 plasm, such constancy can be maintained in the physio- 

 logical environment of the secreting epithelium as will 



