THE NERVOUS REGULATION OF RESPIRATION 531 



to paralyze its skeletal musculature,^ the phrenic nerves were cut and 

 their central ends connected with a galvanometer. It was found that 

 these nerves continued to conduct action currents in a centrifugal 

 direction, clearly indicating thereby a rhythmic activity on the part 

 of the respiratory center. The chemicophysical causes underlying this 

 automatism are wholly unknown, i.e., we have almost no conception 

 regarding the manner in which the metabolic activity of neuroplasm 

 can give rise to a nervous action of this kind. 



When speaking of the respiratory center, we frequently lose sight 

 of the fact that this structure has to fulfill a double function, because 

 it activates not only the muscles of inspiration but also those of 

 expiration. To be sure, under normal conditions only the former are 

 brought into play, while the latter remain passive, but conditions may 

 arise at any time which make it imperative to increase the pulmo- 

 nary ventilation by an active participation of the expiratory muscles. 

 It may be assumed, therefore, that the respiratory center consists 

 in reality of two parts, namely, of an inspiratory and an expiratory. 

 It is conceivable that the function of this entire aggregation of nerve 

 cells is distributed in such a way that the control of the inspiratory 

 muscles is apportioned to some of them, while others are concerned 

 exclusively with the expiratory process. This view may be justified 

 by certain experimental evidence, in spite of the fact that the separate 

 existence of an expiratory center has not been proven. At all events, 

 it is evident that the activity of these cells does not conflict with the 

 function of those controlling the inspiratory mechanism; in fact, it is 

 really subordinated to that of the latter. Thus, active expiratory ef- 

 forts are invariably made when the venosity of the blood is increased, 

 the purpose of these being to aid the inspiratory mechanism in remedy- 

 ing this condition. In a volitional way, the expiratory mechanism is 

 brought into play during the acts of micturition, defecation, parturi- 

 tion, coughing and sneezing, and in all these instances the inspiratory 

 mechanism is made to conform absolutely to the expiratory. Such an 

 interaction gives rise to the so-called ''abdominal press," which plays 

 an important part in the expulsion of the feces and urine. 



The Regulation of the Activity of the Respiratory Center. — Since 

 it has been shown that the power of automaticiiy is restricted to the 

 respiratory center, it should now be evident that the inspiratory 

 movements must cease whenever the muscles expanding the thorax 

 are separated from it. It will be seen, therefore, that the respiratory 

 mechanism differs somewhat from that controlling the activity of the 

 heart, because while the latter organ is also regulated by an automatic 

 center, it possesses the power of continuing its contractions even after it 

 has been separated from the central nervous system. Thus, unlike the 

 respiratory muscles, the heart is capable of developing an automaticity 

 of its own. Keeping these facts clearly in mind, the further statement 

 may now be made that the automaticity of the respiratory center may 



^ Winterstein, Pfltiger's Archiv, cxxxviii, 1911, 159. 



