298 RESPIRATION. 



in pure hydrogen gas ; 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 carbonic acid. For while 

 1000 grammes' weight of frogs exhaled about 0.071 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 on the admission of air after remaining for 

 about half an hour in a nearly complete vacuum ; and that if they were 

 killed by total abstraction of the air, 1000 grammes' weight of the ani- 

 mals were found to have eliminated 0.600 gramme of carbonic acid. 

 Similar facts were previously observed by Spallanzani ; and Paul Bert 

 found that while a certain quantity of fresh muscular tissue, in atmo- 

 spheric 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 to go on, 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. 1 



It is furthermore evident that in this process of internal respiration 

 by the tissues, as in the external phenomena of respiration by the lungs, 

 the quantities of oxygen absorbed and of carbonic acid exhaled do not 

 always bear the same relation to each other. This is shown by the ex- 

 periments of Paul Bert on the gases absorbed and discharged by the 

 different tissues of the dog in contact with atmospheric air, where 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 each case. 



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



QUANTITY OP AND C0 a ABSORBED AND EXHALED DURING 24 HOURS, 



IN CUBIC CENTIMETRES. 

 By 100 grammes of Oxygen absorbed. Carbonic acid exhaled. 



Muscle 50.8 56.8 



Brain 45.8 42.8 



Kidneys 37.0 15.6 



Spleen 27.3 15.4 



Testicles 18.3 27.5 



Pounded bones .... 17.2 8.1 



The production of carbonic acid by the tissues is not, therefore, di- 

 rectly connected with the absorption of oxygen. The precise chemical 

 action by which carbonic acid originates in the solid organs is unknown ; 

 but it is probably by some mode of decomposition in which a portion 

 of the carbon and oxygen present in the tissues separate from their 

 previous combinations in this form, while the remaining elements at the 

 same time unite to produce other substances of different composition. 



The process of respiration consists, accordingly, in an interchange of 



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



