124 RESPIRATION L.ECT. VI. 



ide of azote are capable of maintaining respiration for a few 

 minutes. Perhaps, in oxygen gas this function would be 

 maintained for a considerable time, were it not that by 

 breathing this gas the respiratory movements become more 

 frequent, the arterial pulsations quicker, and the blood every 

 where acquires a very bright red colour. In protoxide of 

 azote respiration may be continued for a few minutes with- 

 out any serious inconvenience ; but, as in the case of oxy- 

 gen, the respiratory movement is accelerated, the cerebral 

 functions become disturbed, and a kind of drunkenness 

 ensues. 



We are now acquainted with the phenomena which take 

 place during respiration, both in the air itself and in the 

 organism ; oxygen is absorbed, carbonic acid is exhaled, 

 black venous blood is changed into red arterial blood, and 

 these two modifications occur in the same organ, where, 

 from its peculiar structure, the atmospheric air, which yields 

 up its oxygen, and the venous blood which becomes red, 

 are nearly in contact, or separated only by an extremely 

 thin membrane. 



Respiration is a physico-chemical process. Are these mo- 

 difications of the air and the blood, phenomena which occur 

 in living beings only ? Do we find, that any changes ana- 

 logous to those which happen during respiration, ever take 

 place between atmospheric oxygen and venous blood drawn 

 from a living being ? The most simple experiment will 

 soon answer these queries, and leave no doubt in your minds 

 of the absolutely physico-chemical nature of this function. 



Here I have a mass of blood which has been coagulated 

 for several hours : you perceive that its surface is red, 

 while that of the piece which I cut off is blackish ; but be- 

 fore many minutes have elapsed it becomes red. I direct 

 some carbonic acid upon the red surface of this clot, and 

 it becomes almost immediately black. I pass a current of 



