AND ANIMAL LIFE. 17 



extent. The same remarks will also apply to the 

 blood circulating in the lungs. If we consider 

 the favourable disposition of this organ for the 

 reception of the vital fluid, we shall be persuad- 

 ed that the portion which is transmitted by the 

 right ventricle is not that portion which is im- 

 mediately expelled by the left : several times 

 this quantity must be exposed to the action of 

 the air : and it is probable that this has its de- 

 grees of oxygenation, according to the rank 

 which it occupies in the series of changes or pul- 

 monic capillary circulation. This view explains 

 why the causes, which prevent the free return of 

 blood to the lungs, do not deprive the heart, in 

 the same ratio, of that which flows along the 

 arteries. If the heart depended on this delicate 

 adjustment or harmonious action, its function 

 would be continually liable to derangement, not 

 only on extraordinary occasions, as at present, 

 but almost on every trifling occurrence affecting 

 the system. 



XXV. The blood possessing more stimulat- 

 ing qualities when expiration preponderates, the 

 heart participates in this improvement ; its con- 

 tractions are more vigorous, from its cavities 

 being excited ; and, therefore, when the acts of 

 expiration have become more moderate, or when 

 their exclusive character has subsided, the arte- 

 rial system retains, for some time, a superior 

 energy of function, indicated by fulness or 



15 



