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), ie., 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 1 c.c. from the respiratory chamber. There- 
fore this nerve for ro mg. for ten minutes’ respiration 
will not give any precipitate when we take 2.1 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 
