THE BIOMETER: HOW TO USE IT 



123 



the' stimulated nerve is placed. Later the total amount 

 of the precipitate grows much larger on the drop in this 

 chamber. This clearly shows that the chamber in which 

 the larger amount of the precipitate is found must have 

 the higher concentration of carbon dioxide. Since we 

 had exactly the same kind of air at the beginning, the 

 conclusion is that the nerve when stimulated must give 

 off more carbon dioxide than the resting one. This 

 conclusion can easily be confirmed by exchanging the 

 nerve in the chambers as usual. 



The following figures will illustrate the different stages 

 of the granulation of barium carbonate and will show 



i 23 4 5 50 o 



FIG. 4. Different stages of the granulation of barium carbonate on 

 the surface of the hemispherical drop of barium hydroxide; $a and 6a 

 show the top views of the drops at the time when "iris effect" is pro- 

 duced. 



definitely how easy it is to compare the amount of carbon 

 dioxide production at several points. And such com- 

 parison can be confirmed more exactly by the quantita- 

 tive determination ; the details of the method are given in 

 the next paragraph. 



The method for quantitative measurement of carbon 

 dioxide. While the apparatus is drying, prepare the 

 tissue and weigh it. If everything is perfectly dry, fill 

 both chambers with mercury up to the marks, as directed 

 on p. 118. Remove the stopper from the right chamber 

 only, which is to be used as a respiratory chamber, 

 and the tissue is to be left in this; the other chamber 



