262 THEORY OF RESPIRATION. 



can possibly be formed by the oxygen absorbed in the 

 lungs. 



The hypothesis just developed rests on well-known 

 observations, and, indeed, explains completely the pro- 

 cess of respiration, as far as it depends on the globules 

 of the blood. It does not exclude the opinion, that 

 carbonic acid may reach the lungs in other ways ; that 

 . certain other constituents of the blood may give rise to 

 the formation of carbonic acid in the lungs. But all 

 this has no connexion with that vital process by which 

 the heat necessary for the support of life is generated 

 in every part of the body. Now it is this alone which, 

 for the present, can be considered as the object truly 

 worthy of investigation. It is not, indeed, uninterest- 

 ing to inquire, why dark blood becomes florid by the 

 action of nitre, common salt, &c. ; but this question has 

 no relation to the natural respiratory process. 



The frightful effects of sulphuretted hydrogen, and 

 of prussic acid, which, when inspired, put a stop to all 

 the phenomena of motion in a few seconds, are ex- 

 plained in a natural manner by the well-known action of 

 these compounds on those of iron, when alkalies are 

 present ; and free alkali is never absent in the blood. 



Let us suppose that the globules lose their property 

 of absorbing oxygen, and of afterwards giving up this 

 oxygen and carrying off the resulting carbonic acid ; 

 such a hypothetical state of disease must instantly be- 

 come perceptible in the temperature and other vital 

 phenomena of the body. The change of matter will 



