110 



Dr. W. Marcet. On the Chemical 



[Jan. 15, 



[This amounts to 225 c.c. C0 3 , which have been retained in the 

 blood ; but it occurs to me that less oxygen may possibly be consumed 

 from re-breathed air than from fresh air, although in my experiments 

 re-breathing is hardly carried far enough to admit of such a contin- 

 gency. Jan. 22.] 



We find, by a consideration of the next table, that the reduced 

 elimination of carbonic acid in re-breathed air is regulated in a 

 marked degree by the weights of C0 2 expired in ordinary breathing. 



Thus it is seen that the CO 2 in re-breathed air and in ordinary 

 breathing increase together from the lowest to the highest figures. 

 This might have been expected, as the whole experiment must be con- 

 trolled more or less by the phenomena of ordinary breathing for each 

 of the persons under experiment. 



There is another point of interest to be noticed with reference 

 to the re-breathed air in the present experiment the volume of this 

 air, which originally was 35 litres, is no longer 35 litres at the con- 

 clusion of the experiment, but has undergone a slight reduction. The 

 enquiry into this portion of the subject was not found so simple as it 

 appeared to be at first, and, as the work progressed, precautions 

 against errors had to be taken which had not been apparent until a 

 late period of the investigation. I, therefore, prefer to leave this 

 part of the subject for future consideration. 



It has been stated that after re-breathing for five minutes the air 

 of the bell-jar, and then admitting fresh air into the lungs, an in- 

 creased volume of air was inhaled attended with the expiration of a 

 greater amount of carbonic acid than in ordinary breathing. This 

 will be seen in the following table, showing, for the same lapse of 

 time, the mean results obtained on four different persons for ordinary 

 respiration and while inhaling fresh air, immediately after the re- 

 breathing stage of the experiment. 



A consideration of these tables shows, with reference to the C0 3 

 expired, that there was invariably an excess, after re-breathing air 

 for five minutes, over the weight expired in the same time in normal 

 respiration; the mean relation being 1 to T237. In the case of 



