RESPIRATION 219 



nerves connected with the region between the two planes of 

 section divided, any interference with the gaseous exchange 

 in the lungs is at once followed by dyspnoea.* 



The question has been raised whether, in the absence of 

 this ' natural ' stimulation by the blood, and of the impulses 

 that constantly reach the centre along its afferent nerves, it 

 would continue to discharge itself, or whether it would sink 

 into inaction. We have already discussed a similar question 

 in regard to the cardiac and vaso-motor centres, and the 

 subject must again present itself when we come to examine 

 the functions of the central nervous system. In the mean- 

 time it is only necessary to say that the apparent auto- 

 matism of the respiratory centre, although modified by 

 the quality of the blood which circulates in it, is not essen- 

 tially dependent on it ; for in animals whose blood has been 

 replaced by normal saline, or serum, and in frogs after 

 excision of the heart, quiet, regular breathing has been seen. 



Action of Drugs on the Respiratory Centre. The respiratory 

 centre is directly affected by numerous drugs. Pituri and nicotin, 

 for instance, cause in various animals a quickening and deepening 

 of the respiration, followed, if the dose has been large, by slowing 

 and ultimate cessation. The action of the great majority of such 

 substances, however, possesses only a pharmacological interest, and 

 it would be out of place even to enumerate them in a text-book of 

 physiology. But there are one or two points in the action on the 

 respiratory centre of chloroform and alcohol substances so greatly 

 employed in practical medicine and in physiological research which 

 may properly be touched on here : 



Chloroform. The cause of the deaths from chloroform which, at 

 rare intervals, startle the operating theatre of every great hospital 

 where this anaesthetic is used, has been, on account of its extreme 

 practical interest, the subject of prolonged discussion and experiment. 

 Is it the heart that fails ? Or is it the respiration ? The answer of 

 what is known as the ' Edinburgh School ' is that the respiration (in 

 physiological terms, the respiratory centre) is always first paralyzed. 

 Their golden rule of doctrine in chloroform administration is, 

 4 Watch the respiration; the heart will take care of itself a rule 

 which, however, in ' Edinburgh ' practice does not exclude careful 

 observation of the pulse. This view, having the merit of simplicity, 

 has been widely adopted. It has been lately upheld by a scientific 

 commission appointed by the Nizam of Hyderabad to investigate the 

 question with the aid of modern physiological methods. But the 

 conclusions of the Hyderabad Commission seem to have been too 



* The conclusion is doubtless correct, but this experiment is not 

 decisive. For the phrenic nerves themselves contain afferent fibres, 

 through which the respiratory centre might have been affected. 



