CHEMICAL PHENOMENA OF RESPIRATION. 333 



excitation, produced by an excess of carbonic acid, apparently 

 is chiefly in those nervous centres which govern respiration 

 (and which we shall study shortly : the medulla oblongata, 

 or bulb) ; the over-excited respiration then becomes hurried, 

 and much more forcible than before, as is observed in cases 

 of dyspnoea. On the other hand, when the blood contains a 

 large quantity of oxygen, the (central) desire to breathe 

 (besoin de respirer) is less strongly felt, and respiration ceases 

 or becomes imperceptible : for instance, if artificial respiration 

 be produced in an animal, in such a manner as to accumulate 

 an excess of oxygen in the blood, the desire to breathe is no 

 longer experienced in the nervous centres (the medulla 

 oblongata) ; these are not, in this case, excited by the car- 

 bonic acid, and spontaneous efforts at respiration will almost, 

 if not entirely, cease. Similarly let a man make several rapid 

 and deep inspirations : as the blood is now saturated with 

 oxygen, and contains very little carbonic acid, a certain time 

 will elapse before the desire for respiration is felt ; thus divers, 

 after making a number of rapid and deep respirations, can re- 

 main for a certain time in the water, without suffering from, 

 the complete arrest of respiration. 



We see thus that the gaseous exchanges have great influ- 

 ence on the functions of the nervous centres, and especially 

 of the respiratory nervous centre, and that these facts must be 

 taken into account when studying the relation between the 

 nervous system and the production of the mechanical phe- 

 nomena of respiration. 



Returning to the study of the conditions which serve to 

 increase or diminish the respiration of the tissues, or rather, 

 the magnitude of the gaseous exchanges which take place in 

 the lungs, we shall find other differences, depending on con- 

 stitution, age, and sex: a robust person produces more car- 

 bonic acid in a given time than one of a delicate constitution ; 

 a child produces more than an adult of the same weight; 1 



consequently, produces calorification (Cl. Bernard, Cours de 1872). 

 This explains the elevation of temperature observed in corpses a short 

 time after death (especially in persons who have died of cholera). 

 The fact of this increase was formerly disputed, but it has been 

 proved beyond all doubt, and, now that its mechanism is explained, 

 it no longer appears extraordinary. 



1 This is the case with a child, but not with a new-born infant, 

 nor yet with the foetus. The combustion which takes place in the 

 tissues of the latter is much less active: thus the muscles of newly 

 born animals consume, in the same space of time, a much smaller 

 quantity of oxygen than those of adult animals of equal weight 



