1 6 A CHEMICAL SIGN OF LIFE 



method is described in detail in the Appendix. The 

 special apparatus, the biometer, as I have named it, 

 which was constructed for the investigation, is shown in 

 Fig. i, and its use is detailed in the Appendix. It will 

 detect one ten-millionth of a gram of carbon dioxide and 

 estimate it with accuracy. 



As is shown in the figure, the biometer has two 

 respiratory chambers each provided with a small tube, at 

 the top of which the hemispherical drop of barium 

 hydroxide can be formed. Exceedingly minute amounts 

 of carbon dioxide produced in the chamber by the small 

 piece of nerve will be precipitated as barium carbonate 

 on the surface film of these hemispherical drops and may 

 be seen with a lens. As the apparatus has two chambers, 

 not only can we detect very small amounts of carbon 

 dioxide which the nerve may produce, but we can also 

 compare the output of carbon dioxide of different 

 tissues under the same conditions, by placing one 

 tissue in one respiratory chamber and another in the 

 other. 



To discover whether nerve fibers, as distinct from 

 nerve cells, respire, particular care was taken to select 

 at first those nerves which are known to be free from 

 such cells and, as far as possible, free also from connective 

 tissue. It was necessary to do this because the work of 

 several investigators seemed to indicate that tissue oxi- 

 dation was in some way dependent on the cell nucleus. 

 Certain biologists even went so far as to believe that a 

 nerve fiber ought not to respire at all, since it contained 

 no nucleus. The fact that the blood supply to the 

 brain, where most of the nerve cells are located, is so 

 copious, whereas the blood supply to the nerve fibers is 



