202 APPLIED PHYSIOLOGY 



the centre which control the diaphragm and the ribs 

 respectively, so that one or other of these can be thrown 

 out of action without interfering with the other. Thus 

 it is possible for a patient with localized peritonitis to 

 breathe with his ribs only, part or the whole of the 

 diaphragm being kept motionless. It is probable that 

 a like independence is possessed by the different groups 

 of cells in the centre which innervate the muscles which 

 act upon the individual ribs, so that even a limited 

 portion of the chest wall can be thrown out of action 

 if the need arises without disorganizing the rest. 



On the other hand, it seems to be impossible to mark 

 off any part of the centre as being specially connected 

 with inspiration or expiration respectively. 



Much discussion has raged over the question whether 

 the centre can act spontaneously or whether it must 

 always be prompted by influences coming to it from 

 without. The truth would appear to be that whilst the 

 centre is possessed of power of spontaneous action, such 

 power is very rarely put into exercise ; probably, indeed, 

 never at all even in conditions of disease, unless, perhaps, 

 the last gasping breaths of life are to be regarded as 

 evidence of such activity. 



The respiratory centre can be powerfully influenced 

 by two distinct agencies: (1) nervous stimuli, (2) the 

 composition of the blood. We shall consider these 

 separately. 



1. The chief afferent nerves which act upon 

 the centre are the vagi. As regards these, matters 

 seem to be so arranged that each phase of respiration 

 prepares the way for its successor. Collapse of the 



