134 A CHEMICAL SIGN OF LIFE 
The following calculation will make the method 
clearer: . 
The original volume of the respiratory chamber is 
31.4 C.c., to which 6.4 c.c. of mercury are introduced, 
making the remaining volume exactly 25 c.c. Ten 
milligrams of the tissue are used and are allowed to 
respire in the chamber for ten minutes. Then about 
to to 15 cc. of the gas are withdrawn into the 
tube B; 0.5 cc. of this gas gave no precipitate 
during the first ten minutes; 0.5 c.c. more of the 
same sample gave no deposit in another interval of 
ten minutes. Thereupon 0.5 c.c. more, a total of 
I.5 ¢.c., was run into the chamber. A marked evi- 
dence of a precipitate appeared in ten minutes. There- 
fore 1.5 c.c. of this gas must contain 1.0X107’ g. of 
carbon dioxide. 
The apparatus is then cleaned and dried and a clear 
drop of barium hydroxide is again introduced upon the 
top of the tube d; and after making sure that the air is 
free from any carbon dioxide by waiting, 1 c.c. of the 
sample gas which has been left undisturbed in the tube B 
is introduced into the chamber; no precipitate will be 
found to have formed within ten minutes; 0.25 c.c. 
more of the sample will not produce any precipitate; 
but if o.25 c.c. more is taken, crystals of barium car- 
bonate appear after ten minutes. It follows that 1.5 c.c. 
of the respired gas must contain 1.0X1077 g. of carbon 
dioxide. 
From these duplicates it becomes certain that 1.5 c.c. 
of 25 c.c. capacity of the chamber now contain 1.0X 
io’ g. of carbon dioxide. Therefore the total amount 
