AND ANIMAL LIFE. 385 



nary well-marked characters ;* indeed the dis- 

 tinction, in regard to colour, between arterial 

 and venous blood, is almost lost. The cause of 

 these phenomena appears so evident, and so 

 closely connected with the effect, that it is al- 

 most impossible to refer the latter to any other 

 agent than oxygen. If this be granted, we must 

 acknowledge that the principles or powers of 

 life are to be attributed to the influence of this 

 agent. 



CCCCLIX. The blood possessing under va- 

 rious circumstances a greater or less proportion of 

 the vital principle, as indicated by the activity 

 of organic and animal functions, and also by its 

 external qualities, it necessarily follows, if it be 

 highly oxygenated, and characterized by a variety 

 of effects in the living system, that it ought also, 

 when removed, to be distinguished from that 

 which is in a different condition, if both be 

 placed in precisely the same situation. I have 

 already observed that the circulating fluid in the 

 child possesses a greater portion of vitality than 

 the same in one advanced in years ; and the cor- 

 rectness of this opinion is demonstrated by the 

 following experiments of HUNTER, instituted, 

 not for the purpose of proving the present 

 point, but in order to ascertain the difference in 

 the properties of the blood at different ages. 



Vide Chap. VIII. 



B b 



