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 

 10 to 15 c.c. of the gas are withdrawn into the 

 tube B; 0.5 c.c. 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 

 1.5 c.c., was run into the chamber. A marked evi- 

 dence of a precipitate appeared in ten minutes. There- 

 fore i . 5 c.c. of this gas must contain i . oX io~ 7 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, i 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 0.25 c.c. more is taken, crystals of barium car- 

 bonate appear after ten minutes. It follows that i . 5 c.c. 

 of the respired gas must contain i.oXio" 7 g. of carbon 

 dioxide. 



From these duplicates it becomes certain that i . 5 c.c. 

 of 25 c.c. capacity of the chamber now contain i.oX 

 io~ 7 g. of carbon dioxide. Therefore the total amount 



