RESPIRATION. 



the tissues. Every organized tissue, in the recent condition^ba$*tsi ** 

 power both of absorbing oxygen and of exhaling carbonic acid. 

 Liebig showed that frogs' muscles, recently prepared and freed from 

 blood, will absorb oxygen and discharge carbonic acid. Similar exper- 

 iments with other tissues have led to the same result. It is in their 

 substance, accordingly, that the oxygen is consumed, and the carbonic 

 acid takes its origin. But these two phenomena are not immediately 

 dependent on each other. In some instances, living animals as well as 

 fresh animal tissues will continue, for a time, to exhale carbonic acid 

 in an atmosphere of hydrogen or of nitrogen, or even in an exhausted 

 receiver. Marchand found that frogs would live from half an hour to 

 an hour in pure hydrogen ; and that during this time they exhaled even 

 more carbonic acid than in atmospheric air, owing probably to the 

 superior displacing power of hydrogen for this gas. While 1000 

 grammes' weight of frogs exhaled about 0.077 gramme of carbonic 

 acid per hour in atmospheric air, they exhaled during the same time 

 in pure hydrogen as much as 0.263 gramme. The same observer 

 found that frogs would recover after having remained for about half 

 an hour in a nearly complete vacuum ; and that, when killed by the 

 total abstraction of air, 1000 grammes' weight of the animals had 

 eliminated 0.600 gramme of carbonic acid. Similar facts were observed 

 by Spallanzani ; and Paul Bert * found that while a certain quantity of 

 fresh muscular tissue, in atmospheric air, exhaled, in a given time, 30 

 cubic centimetres of carbonic acid, the same quantity, in pure hydrogen 

 exhaled 23 cubic centimetres during the same time. He even found 

 that the exhalation of carbonic acid would continue, in an atmosphere 

 of nitrogen, from muscular tissue which had previously been subjected 

 for a quarter of an hour to the action of a vacuum. 



It is, furthermore, evident that in this internal process, as in the 

 external phenomena of respiration by the lungs, the quantities of oxy- 

 gen absorbed and of carbonic acid exhaled are not always in the same 

 relation. Thus in the experiments of Bert on the gases absorbed and 

 discharged by the tissues, in some instances the volume of carbonic 

 acid produced was greater, and in others less than that of the oxygen 

 consumed ; the proportions of the two varying considerably in differ- 

 ent cases. 



The following list gives the result of a series of these experiments : 



QUANTITY OF AND CO 2 ABSORBED AND EXHALED DURING 24 HOURS, 

 IN CUBIC CENTIMETRES. 



Lecons sur la Physiologic comparee de la Kespiration. Paris, 1870, p. 49. 



