1891.] Formation of Carbonic Acid in Human Respiration. 65 



same proportion whatever the volume of air expired. By this means 

 the results obtained for the volumes of oxygen consumed and absorbed, 

 which are the main objects of the present enquiry, are thoroughly 

 reliable. 



The experiments are made 011 two different persons, and show that 

 not only the carbonic acid expired within a given time but also the 

 oxygen consumed varies according to individuals. The subjects of these 

 experiments are well suited to show " extremes " as to the function of 

 respiration, one of them being 63 years of age and the other 21, both 

 in perfect health. 



Twelve experiments were made in both cases, six while under the 

 influence of food and six while fasting. No experiments were made 

 under extreme fasting.* 



On considering the Tables, the composition per cent, of the air 

 expired is observed to alter but little. In my case the CO 2 varies 

 from 4-53 to 5'14. 



The proportion of oxygen was very constant, ranging also with me 

 from 15-30 to 16'0. 



The volumes of oxygen consumed represented the volumes of 

 oxygen the body took up, on one hand for the combustion and 

 elimination of carbon in the form of carbonic acid, on the other, for 

 the probable elimination of tissues in the form of crystalloid com- 

 pounds. The relations between the oxygen consumed and the 

 carbonic acid produced varied in my case between 0'816 and 0'912 

 with a mean of O863. 



The proportion of the oxygen consumed which is absorbed is easily 

 found by subtracting the volume of C0 2 produced from the total volume 

 of oxygen consumed. This volume has been expressed as absorbed per 

 minute, a result obtained by dividing the figure found by the number 

 of minutes and seconds the experiment lasted. The volumes ab- 

 sorbed per minute varied in my case from 21 - 3 to 42'8 c.c., with a 

 mean of 33'0 c.c. ; this was equal to 2'83 grams of oxygen absorbed 

 per hour. It may be concluded that this absorption of oxygen is an 

 important factor towards the phenomena of nutrition. 



The proportion of oxygen absorbed in my case for 100 parts of air 

 inspired exhibits a mean of 0'74 part, and varies from 0'44 to 

 1*03. This does not agree with the volume of oxygen usually con- 

 sidered as absorbed, amounting to about 2 per cent. The correspond- 

 ing proportion for the experiments on Mr. Russell will be found nearly 

 exactly that obtained for myself, and I must conclude that 0'74 

 per cent., or a closely approximating figure, shows the proportion of 

 the air inspired (in the form of oxygen) which remains in the 

 blood, and consequently does not reappear in the corresponding all* 



* See Tables accompanying this paper. 

 VOL. L. P 



