484 RESPIRATION. 



It is due to a want of oxygen on the part of the system, 

 and not to any fancied irritant properties of carbonic acid ; 

 for when the lungs are filled with air, and the system is grad- 

 ually drained of blood, though all the blood which finds its 

 way to the capillaries is fully oxygenated, as the quantity 

 becomes insufficient to supply the required amount of oxygen, 

 the sense of want of air is felt, and respiratory efforts take 

 place. The experimental results on which these conclusions 

 are based are invariable, and have been demonstrated re- 

 peatedly ; so that the location of the respiratory sense in the 

 general system, and the fact that it is an expression of a want 

 of oxygen, seem as certain as that oxygen is taken up by the 

 blood from the lungs, and distributed to the tissues by the 

 arteries. With this view we can explain all the reflex phe- 

 nomena which are connected with the respiratory function. 1 



The supposition of Berard that the respiratory sense is 

 due to distention of the right cavities of the heart is disproved 

 by the simple experiment of sudden excision of this organ. 

 In that case, as the system is drained of blood, efforts at 

 respiration invariably take place, though the supply of air to 

 the lungs be continued. 



Sense of Suffocation. We must separate, to a certain 

 extent, the respiratory sense from the sense of distress from 

 want of air, and its extreme degree, the sense of suffocation. 

 The first is not a sensation, but an impression conveyed to 

 the medulla oblongata, giving rise to involuntary reflex move- 

 ments. The necessities on the part of the system for oxygen 

 regulate the supply of air to the lungs. We have already 

 seen that every five to eight respirations, or when the respi- 



1 There are many phenomena which physiologists found it impossible to ex- 

 plain on the supposition that the " besoin de respirer" was located in the lungs and 

 conveyed to the medulla oblongata by the pneumogastrics ; among which may 

 be mentioned the effect of irritation of the general surface in the resuscitation of 

 new-born children in which respiration is not established spontaneously. Dr. 

 Marshall Hall and John Reid thought that in these cases the sensory filaments dis- 

 tributed on the skin had something to do in transmitting impressions to the respi- 

 ratory centre. 



