330 



THE RESPIRATION 



by them to the respiratory center. By such an operation the only lower 

 respiratory neurons left intact are those of the phrenic nerve, so that the 

 respiratory movements that alone are possible are those in which the 

 diaphragm participates and the muscles of the alse nasi and larynx. It 

 was found that the animal after the operation went on respiring, though 

 imperfectly, and that the respirations soon became more marked and 

 asphyxial in character, indicating that the blood was not becoming 



Diaphraym. 



Fig. 120. Diagram to show where cuts are made to isolate the chief respiratory center from 



afferent impulses. 



properly aerated and that the chemical changes occurring in it were 

 acting directly on the center, stimulating it to greater activity. The 

 conclusion seems warranted that the respiratory center can act auto- 

 matically, for the only possible afferent nerves left in the above prepara- 

 tion were those carried to the center by the fifth nerve (Fig. 120). 



That the respiratory center is extraordinarily sensitive to changes in 

 the composition of the blood flowing through it is a fact that has been 

 known for a long time, but it is only within recent years that the exact 



