INVESTIGATIONS ON METABOLISM. 93 
METHODS OF ANALYSIS. 
The methods used for the analysis of the food and feces 
were in general those adopted by the Association of Official 
Agricultural Chemists. Certain deviations were introduced 
where necessary. ‘The methods used for the analyses of urine 
were such as are commonly followed. The methods employed 
in the determinations of water and carbon dioxide in the 
incoming and outgoing air involved some special deviations 
from those ordinarily in use. 
PREPARATION OF SAMPLES. 
Meats, vegetables, and other materials containing consider- 
able water require to be chopped or otherwise comminuted 
and partially dried before grinding. For comminuting meats 
we use an ordinary sausage grinder. The ‘‘ Excelsior Meat 
Grinder’’ has proved very satisfactory for this purpose. 
Potatoes, when fresh, are cut in thin slices with a knife. 
When cooked they are simply mashed. Bread is easily 
sliced, broken, and pulverized sufficiently for the purpose. 
The samples when too moist for grinding were partially 
dried; the material in the original or partially dried form was 
sampled and ground, first in an ordinary ‘‘ Excelsior Mill,”’ 
afterwards in a Maercker-Dreefs Mill, by which it is easily 
reduced to an impalpable powder. 
CARBON DIOXIDE AND WATER IN AIR. 
In experiments of the class to which these belong the respir- 
atory products commonly determined are carbon dioxide, water 
and volatile organic compounds. 
The determination of carbon dioxide is most essential and is 
of course always attempted. The experience of a number of 
experimenters during the past twenty-five years implies that 
the difficulties in the way of fairly accurate results are not 
insuperable. ‘he carbon dioxide given off in respiration is 
quickly diffused through the air and readily conveyed away by 
the ventilation current so that the accurate measurement of 
that current and determination of the percentage of carbon 
dioxide suffices for the ordinary purposes of experiment. Ii, 
therefore, the accurate measuring and sampling of the air are 
provided for, a correct method for determining the carbon 
dioxide in the sample is all that is needed in addition. 
