DELICACY OF ORGANIC REGULATION 49 



Eustachius, who was probably the first to 

 make experiments on secretion by the 

 kidneys, contented himself with taking a 

 dead, and probably decomposing, kidney, 

 and passing through its blood-vessels such 

 liquids as spirits of wine or water, and 

 observing how much of these liquids issued 

 into the ureter ! It is only quite recently 

 that we have come to realise the astounding 

 fineness with which the kidneys, respiratory 

 centre, and other parts regulate the composi 

 tion of the blood. 



To illustrate this point I may perhaps refer 

 to a subject which we have recently been 

 investigating at Oxford. We have found 

 that the respiratory centre is so extremely 

 sensitive to any increase or diminution of the 

 partial pressure of carbon dioxide in the blood 

 that a diminution 0*2 per cent, of an atmo 

 sphere, or 1*5 mm. of mercury will cause 

 apncea, while a corresponding increase will 

 double the breathing. The recent researches 

 of Hasselbalch have afforded experimental 

 evidence of what had already seemed very 

 probable that the stimulus to which the 

 centre responds is the difference in hydrogen 



