THE BIOMETER: HOW TO USE IT 127 



vary it, for it is not only a waste of time to try to get 

 exactly the same amount of the tissue for each experi- 

 ment, but in many cases such an attempt will lead to 

 a number of physiological errors. Of course there is a 

 time when we must select the same weights of the tissues 

 for a particular experiment, such, for instance, as when 

 we are to test the relation of the sizes of the tissue and 

 rate of the carbon dioxide production. 



The quantitative experiments, therefore, consist in 

 determining the least volume of the gas necessary to give 

 the precipitate for a known weight of the tissue for a 

 known period of time. This can be found by experi- 

 menting on several tissues of different weights (too much 

 variation of the weight should be avoided), i.e., by 

 obtaining two sets of results, namely, the one which does 

 not give the precipitate and the other which gives the 

 precipitate. 



These results are calculated on the standard unit, so 

 that we can compare them with each other. We have 

 usually taken 10 mg. and ten minutes as units. An 

 example will explain: 14 mg. of the nerve for fifteen 

 minutes of respiration did not give a precipitate when 

 we took but i c.c. from the respiratory chamber. There- 

 fore this nerve for 10 mg. for ten minutes' respiration 

 will not give any precipitate when we take 2 . i c.c. from 

 the chamber. In another case we took 13 mg. of the 

 nerve, which after ten minutes' respiration produced so 

 much carbon dioxide that 2 c.c. gave a precipitate; 

 thus 2 . 6 c.c. will give precipitate for 10 mg. of the nerve 

 for ten minutes' respiration. In this way a series of 

 experiments with several fresh nerves was conducted in 

 order to approximate both the minimum volume which 



