CHAPTER III 



The Nervous Control of Breathing. 



It is now necessary to discuss more closely the influence of nervous 

 control on breathing. The rhythmic activity of the respiratory 

 center is for short periods of time very completely under volun- 

 tary control — a fact evidently connected with the very delicate 

 use of the lungs in phonation, as well as in other voluntary acts not 

 directly connected with "chemical" respiratory functions. Excita- 

 tion of various afferent nerves may also excite or inhibit inspira- 

 tion or expiration. Most of the effects thus produced appear to be 

 protective in various ways, or preparatory to some particular 

 effort, and they only disturb the main regulation of breathing 

 occasionally, just as voluntary interference does. In view of the 

 facts with regard to the control of breathing by chemical stimuli, 

 we might thus be led to the conclusion that the respiratory center, 

 when not interfered with by voluntary or other occasional nervous 

 disturbances, acts simply by producing rhythmic inspiratory and 

 expiratory discharges, determined in extent and frequency by 

 nothing but chemical stimuli dependent on the blood supply. 



This simple conception is entirely inadequate, in view, more 

 particularly, of the facts discovered originally by Hering and 

 Breuer, and already referred to. These facts, apart from the 

 results of section of the vagi, can be observed very fully in man, 

 without the complications introduced by anaesthetics, and were 

 so studied in 191 6 by Mavrogordato and myself.^ We employed 

 a very simple arrangement which enabled us to breathe through 

 a wide-bored tap, and observe by a water manometer the pres- 

 sure between the mouth and the tap when the latter was closed, 

 the nostrils being closed by a clip. If the tap was closed at 

 the end of natural or forced inspiration or expiration, or in 

 any other phase of respiration, the phenomena could be studied. 

 By connecting the far end of the tap with a reservoir containing 

 pure air or air containing any required percentage of CO2, we 

 could observe the influence of hyperpnoea due to CO2, and by 

 suitable volume recorders connected with the far ends of the 

 reservoir and gauge the breathing and pressure could be recorded. 



If wtpiration is interrupted by turning the tap, and all voluntary 



^ Journ. of Physiol., L; Proc. Physiolog. Soc, p. xli, 19 16. 



