CHEMICAL CEPTORS 117 



of the blood. Increase in the H-ion concentration of 

 the blood stimulates the respiratory center and, simul- 

 taneously, inhibits the cortical or driving portion of 

 the brain. In part, increased H-ion concentration is 

 produced by the driving action of the higher brain 

 centers, the acidity being in part overcome by carbon 

 dioxid elimination in respiration. Other important 

 acid-reducing factors will be noted later. Hence, we 

 find an antithetic or balanced reaction between the 

 cortex and the medulla as a result of changes in H-ion 

 concentration ; the cortex increasing the production 

 of acidity, the medulla decreasing it by increasing acid 

 neutralization. Thus, in the midst of an activating 

 environment, the normal alkalescence is maintained. 



There is evidence also that there exists in the brain 

 a mechanism which activates the organs of the kinetic 

 system 1 to the end that the chemical purity of the 

 body may be maintained when foreign proteins are 

 present, exactly as the same organs are driven in re- 

 sponse to contact and distance ceptor stimulation. 

 These points will be taken up later. 



1 See Chapter VI, The Kinetic System. 



