BLOOD. 131 



average, ^yas equal to 21-8 litres/ and the entire volume of 

 the air expired per hour on an average equal to 540 litres. 

 These results agree well with those of the earher observers. 

 When the corrections for moisture are made, the quantity of 

 carbon expired per hour is equal on an average to 172 grains, 

 and of carbonic acid 23-5 litres. 



B. Relations of the constituents of the expired air to the 

 theory of respiration. 



On this point Brunner and Valentin only have experimented. 

 They found — 



Individual. No. of experiments. Volume per cent. Volume per cent, in relation 



to the atmosphere. 



Mean of CO^. O. N. Disappeared O. Difference of N. 



Brunner / 12 exp. 1st series 4-356 16007 79-547 4720 + 0-362 



1 4 exp. 2d „ 3-825 16-300 79-869 4-508 + 0-683 



Thomas . 4 exp. 1st „ 4-673 15-895 79-432 4-920 + 0-329 



Valentin \ ^ ^^^- ^^^ " "^'^^^ \&-\^^ 79-541 4-671 + 0-356 



1 12 exp. 2d „ 4-641 15-783 79-576 5-032 + 0-391 



Total average 4-380 16-033 79587 4-783 + 0-402 



Weight per cent. 



Brunner J 12 exp. 1st series 6-522 17-428 76-050 5-582 — 0-940 



1 4 exp. 2d „ 5-749 17735 76516 5-275 — 0-474 



Thomas . 4 exp. 1st „ 6-975 17-165 75-860 5-845 — 1-130 



Valentin I ^ ^^^- ^^* " ^'^'"^ ^^'^^^ '^'^^^ ^"^^9 — 0-929 



1 12 exp. 2d „ 6-945 17-089 75-965 5-920 — 1-025 



Total average 6-546 17373 76-081 5-637 — 0-909 



It is thus evident that the variations observed in the 

 amount of nitrogen are entirely within the errors of observa- 

 tion, and the nitrogen may be disregarded in the process. 



Again, the expired air contains a volume of carbonic acid, 

 which is but little less than the volume of oxygen which has 

 disappeared (therefore the weight per cent, of the carbonic acid 

 is necessarily somewhat greater than that of the absorbed oxygen, 

 and thus also the difference of nitrogen appears positive as 

 regards volume, but negative as regards weight) ; so that all 

 the oxygen absorbed reappears as carbonic acid, except a small 

 quantity consumed in the body for other pm-poses. Now, 

 according to Graham^s law of the diifusion of gases, when they 

 are separated by an animal membrane and are under equal 

 pressure, they become mixed inversely as the square roots of 



[' The litre is a little larger than the English wine quart ; the litre being equal to 

 •1-028, and the quart to 57-75 cubic inches.] 



