CO-ORDINATING MECHANISMS 11 



from the intestines, it is rapidly got rid of 

 through increased excretion by the kidneys : 

 while diminished excretion balances excessive 

 withdrawal of water from the blood, as by 

 sweating. The kidneys respond in a similar 

 manner to excess of urea, sugar, inorganic 

 salts, acids, or alkalies, etc., the result being 

 that the normal composition of the blood is 

 kept constant within small limits. Another 

 similar case is that of the liver, which forms 

 or discharges various important substances in 

 response to chemical stimuli conveyed through 

 the blood. Physiological investigation is con 

 stantly discovering new cases in which the 

 activity of one organ is excited by the 

 chemical products of activity in other organs. 

 In all these cases the response follows the 

 stimulus, the cause the effect, with unerring 

 accuracy. Apart altogether from the nervous 

 system, therefore, the body is full of mech 

 anisms for the co-ordination and control of 

 functional activity. The nervous system, 

 indeed, has come in recent years to appear 

 much less important than was formerly 

 supposed in the co-ordination of physiological 

 activity ; and it seems to be only in cases 



