626 Experiments 



per cent, that is, 14.9 cc. per 100 cc. of blood [in original French, 

 110 cc.]) . All that the figures permit us to say is that the carbonic 

 acid always diminished when its original proportion exceeded 38 cc. 

 per 100 cc. of blood. 



The averages, represented, according to the agreement fixed 

 above, by Column 3 of Table XII and by graph CO 2 of Figure 35, 

 indicate a decrease, irregular, it is true, but constant. However, 

 one may say that it is established, as a general fact, that the increase 

 of pressure above normal pressure does not change very consider- 

 ably the carbonic acid content of the blood. The result was quite 

 different, as we have seen, for pressures below one atmosphere; 

 but we had already seen, in the neighborhood of 76 cm., that the 

 carbonic acid varies little, and in the figures of Column 14, for the 

 pressure of 56 cm., we find the very low ones of 2.5 per cent and 

 0.8 per cent. On the contrary, at the pressure of 36 cm., for ex- 

 ample, the blood contains an average of 29.2 per cent of carbonic 

 acid less than at normal pressure, which corresponds to an average 

 loss of 11.4 cc. per 100 cc. of blood. 



The important practical conclusion derived from this fact is 

 that the symptoms observed in men and animals subjected to high 

 pressures cannot be attributed to the effect of carbonic acid. We 

 shall return to this point. 



If now we ask ourselves how it happens that the carbonic acid 

 diminishes for very low pressures, without increasing above one 

 atmosphere, the answer is hard to find. I have, however, settled 

 upon the following explanation. 



The respiratory exchanges are not made, as we say in common 

 parlance, between the blood of the lungs and the air of the atmos- 

 phere. If it were so, this air, containing only very slight traces of 

 carbonic acid, would play in respect to the blood with reference to 

 the carbonic acid the role of a vacuum, and only a very small 

 quantity would remain in the blood. But the exchanges are made 

 between the venous blood and the air of the pulmonary vesicles. 

 Now I found earlier 7 that this air, even after an inspiration, still 

 contains from 6 to 8 per cent of carbonic acid. M. Grehant, 8 who 

 later did the same research by a method quite different from mine, 

 reached a result as near mine as one could desire in such a subject. 

 It is therefore the normal presence of this important proportion of 

 carbonic acid in the air of the alveoli which maintains the usual 

 quantity in the blood; this gas is thus its own obstacle, and one can 

 easily see how an exaggerated pulmonary ventilation, lessening the 



