350 RESPIRATION. 



experiments made in reference to this subject seem nevertheless to 

 prove that a diminution of pressure of the air gives rise to a slight 

 decrease in the quantity of exhaled carbonic acid, whilst an aug- 

 mentation of pressure occasions a slight increase in this gas, and 

 that the absolute pressure of the atmosphere must consequently 

 exert a very subordinate influence on the exhalation of carbonic 

 acid. The animals which were employed for these experiments 

 were, however, quite as lively and as much disposed to eat with the 

 barometer both at 34" and at 22" as at the mean pressure. 



Marchand made several experiments on the condition of frogs, 

 when inclosed in a space from which the air had been almost entirely 

 ivithdrawn. When the air-pump was worked slowly, the animals 

 began to show symptoms of uneasiness, and their bodies swelled 

 at a pressure of 54 m. m. [21*25 inches], and at a pressure of 

 4 m. m. [0*16 of an inch] they exhibited considerable inertia, 

 and many of them became asphyxiated. After remaining for even 

 half an hour in vacuo, the animals recovered on a re-admission of 

 air. If the animals were killed by complete abstraction of air, it 

 was found that 1000 grammes' weight of frogs would eliminate 

 about 0*600 of a gramme of carbonic acid. 



Prout's experiments on the influence of the different periods of 

 the day upon the exhalation of carbonic acid have been repeated 

 by several observers, amongst others by Scharling, Vierordt, and 

 Horn,* who have noticed that the different periods of the day 

 occasion decidedly appreciable differences in this respect. We 

 fully concur, however, with Scharling and Vierordt in referring 

 these differences far more to internal conditions of the organism, 

 such as digestion, -waking and sleeping, &c., than to cosrnical 

 relations, if indeed the later claim any consideration. It would at 

 all events appear from the experiments of these observers, that the 

 influence of the different periods of the day, if the above physical 

 relations be set aside, is reduced to a minimum. It must not, 

 however, be forgotten that the numerous experiments of Bidder 

 and Schmidtf perfectly coincide with those of ChossatJ in show- 

 ing that animals, when fasting, constantly exhale far less carbonic 

 acid during the night than by day, this relation continuing unaltered 

 up to the time of death. As these oscillations were found by 

 Schmidt to cease after the animals had been blinded, they cannot be 

 entirely owing to sleeping and waking ; for although light in itself 



* Op. cit 



t Op. cit., p. 317. 



J Recherches experim. sur I'inamtion. Paris, 1843, p. 07. 



