BLOOD. 139 



mata be closed with oil, they speedily die. The researches of 

 Scheele, Vauqueliu, and Hausmann show that in the respira- 

 tion of insects a portion of the oxygen of the atmospheric air 

 is converted into carbonic acid. 



Trem'anus has observed that the amount of oxygen wliicli 

 is taken up is frequently twice as great as is required for the 

 production of the carbonic acid formed, and that insects always 

 develop nitrogen. Thus a honey-bee, confined in an atmosphere 

 of 272 cubic inches, consumed 13*5 of oxygen, while it only 

 yielded 8"3 of carbonic acid and 5-3 of nitrogen. 



The experiments of Spallanzani and Hausmann tend to 

 prove that the changes produced by worms on the atmospheric 

 air in which they are confined are similar to those effected by 

 insects. 



On the metamorphosis of the hJood. 



All our conceptions of organic life are associated with the 

 idea of continuous change of substance. A constant metamor- 

 phosis is going on in the living blood, which, in fact, may be 

 regarded as the most obvious manifestation of its vitality. 



When it ceases to undergo this metamorphosis, it dies ; indeed 

 the very act of \dtal annihilation is attended with a change in the 

 blood, which we regard as an indication of its plastic power. As, 

 however, life in every manifestation of its varying forms is depen- 

 dent on certain conditions, and cannot exist when they are in- 

 fringed, so it is with the vitality of the blood ; for although there 

 is doubtless an actual inherent power in the blood, it can no 

 longer act when it is deprived of the condition requisite for its 

 maintenance, namely, the reciprocal action of the organism. The 

 blood is not the only portion of the body that undergoes this 

 change ; every organ and tissue is subjected to a similar meta- 

 morphosis, which is presented to us under the general phenomena 

 of nutrition and consumption, (or waste,) and which is dependent 

 on, and effected by, the blood alone ; but since the various tissues 

 present a different chemical composition, and since the different 

 organs separate different matters from the blood, it is obvious that 

 they cannot all modify the cu'culating fluid in the same manner, 

 but that the metamorphosis must vary in some degree with the 

 influence of the nervous system. Two conditions are essentially 

 requisite for the metamorphosis of the blood, namely, circulation 



