THE MECHANISM OF TISSUE RESPIRATION 161 



ig'S° C. For purposes of comparison the results obtained have 

 been grouped together and means taken. 



From these mean results we see that the C0 2 discharge of the 

 frogs kept in nitrogen was practically as great as that of frogs 

 kept in air, and that it was influenced to the same extent by rise 

 of temperature. The lack of oxygen, though at first producing 

 no obvious effect either in the C0 2 discharge or the vitality of 

 the frogs, did so after a time, and the higher the temperature at 

 which the experiment was carried out the sooner were the effects 

 produced. The movements of the frogs became gradually 

 feebler, and then ceased, though the heart continued to beat 

 long after the nervous system was completely paralysed, and 

 the C0 2 discharge continued to some extent even after cessation 

 of heart-beat. At a temperature slightly above zero the frogs' 

 movements continued as long as seven days. At 7 C. they 

 continued for eight hours on an average, and at 12 for five 

 hours; but at 21 they ceased in seventy-two minutes, and at 

 27° in twenty-five minutes. Though the C0 2 discharge persisted 

 for longer than these periods, it slackened off very quickly at 

 the higher temperatures, and so it was found that the total 

 volume of C0 2 given off by the frogs was practically independent 

 of the temperature. There seems to be a more or less fixed 

 volume of C0 2 in the tissues of the frog, and this volume can 

 either come off very slowly at a low temperature, or rapidly at 

 a high one. Aubert did not attempt to fix the volume exactly, 

 but he found that whether the frog were kept in nitrogen for 

 1,383 minutes at 7.9 , for 575 minutes at 11 '8°, for no minutes 

 at 22*8°, or for 35 minutes at 27*5°, it almost always gave 

 off about 200 c.c. of C0 2 (reckoned per kilogram of body 

 weight). 



The C0 2 discharge in a nitrogen atmosphere has been 

 measured also in the case of a snail {Limax agrestis) and a 

 caterpillar {Tenebrio molitor). Thunberg, who carried out these 



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