72 MUSCULAR WORK 
with the common use of these words, they are unsuitable. We prefer the 
far-reaching term post-absorptive. 
We were fortunate in being able to secure a subject who was not made 
unduly uncomfortable by performing a large amount of muscular work on 
an empty stomach, so that in neither the rest nor the work experiments were 
the measurements of the metabolism complicated by the influence of food. 
While it cannot properly be said that during the experiments the entire 
alimentary tract was free from absorbable material, nevertheless, it was to 
a very large extent thus free, so that for all practical purposes we may say 
that the subject was living upon body-material. 
By previous experimenting in this laboratory, it has been shown that the 
character of the post-absorptive katabolism might be considerably modified by 
normal alterations in the diet. It was therefore necessary to obtain a base- 
line both for the character of the katabolism as shown by the respiratory 
quotient and for the amount of the katabolism as determined by the measure- 
ment of the carbon dioxide produced and the oxygen consumed. This base- 
line was determined by making a series of rest experiments each morning 
previous to the experiment with muscular work. 
In order that the picture of the resting katabolism might be more com- 
plete, an attempt was made to secure regularly the urine voided during the 
experimental period. In a research of this kind it is of course necessary to 
assume that the nitrogenous products of the urine collected during an ex- 
perimental period represent the protein disintegration for that period. This 
assumption is liable to many gross errors, particularly in experiments with 
severe muscular work as an after-effect of the work upon protein katabolism, 
or at least the nitrogenous excretion in the urine, has frequently been noticed. 
Analyses have been made of these urines, however, and the results of the 
determinations are reported. 
DETERMINATION OF THE RESPIRATORY QUOTIENT. 
In a study of the character of the katabolism as influenced by muscular 
work, the significance of the respiratory quotient makes it necessary that 
this value should be determined with the greatest accuracy. This is doubly 
difficult inasmuch as the determination of the respiratory quotient is affected 
by errors in the values obtained for both the carbon dioxide and the oxygen. 
The determination of the carbon dioxide produced by man is relatively a 
simple matter, there being a number of excellent methods for this purpose. 
The determination of the oxygen absorption is, on the other hand, very 
difficult, and while several methods are in good repute among physiologists, 
it still remains a fact that extraordinary skill is required on the part of the 
observer to secure reliable results. All of our energies, therefore, were con- 
centrated in an effort to obtain the most exact measurements of these two 
factors. The determinations of the carbon dioxide and the oxygen were 
always verified, the respiration apparatus and the connections with the sub- 
ject were continually tested for tightness, precautions were taken to insure 
the full efficiency of the absorbers, and the calibrations of the meter were 
often checked. Furthermore, the inherent difficulties involved in an altered 
respiratory type and the possible effect of a pumping out of carbon dioxide by 
excessive ventilation were taken into consideration. 
