INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM, 201 
Later INnvesticaTions.—In 1882 North * made experiments . 
upon himself in which a considerable amount of work, mainly walk- 
ing from 30 to 47 miles while carrying a load of about 27 pounds, 
was performed on one day of each experiment. The account of the 
experiments does not give sufficient data for computing the total 
amount of work performed, but it was evidently very considerable 
and resulted-in a marked increase in the excretion of nitrogen. It 
is not possible, however, to determine whether the total food was 
adequate for the work days, but it was no greater then than during 
the periods of rest. 
Argutinsky,f in experiments upon himself, observed as a result 
of rather severe work a very marked increase in urinary nitrogen 
which continued at least three days after the cessation of the work. 
Munk { subsequently criticised Argutinsky’s results on the ground 
that the supply of non-nitrogenous nutrients in his diet was insufh- 
cient. Krummacher § obtained results quite similar to those of 
Argutinsky, but his experiments are open to the same criticism as 
those of his predecessor, namely, an insufficient supply of non- 
nitrogenous nutrients, as he himself points out in a later paper. 
Hirschfeldt || failed to observe any material increase in the nitrogen 
excretion as the result of work upon a diet containing a considera- 
ble excess of food over the amount required for maintenance. This 
was true both upon a diet containing little protein and one abun- 
dantly supplied with this nutrient. 
Pfliiger, like Liebig, regards protein as the sole source of mus- 
cular energy. As yet only a preliminary sketch of his investiga- 
tions has been published. He fed a lean dog upon prepared lean 
meat, that is, upon a nearly pure proteid diet, for seven months. 
The animal remained apparently in perfect health and was able to 
perform a large amount of work. Under the influence of the work 
the excretion of nitrogen was observed to increase somewhat, but 
not sufficiently to account for the energy expended in the work. 
This phenomenon Pfliiger explains by supposing that during work 
* Proc. Roy. Soc., 36, 14. 
+ Arch. ges. Physiol., 46, 552. 
¢ Arch. f. (Anat. u.) Physiol., 1890, p. 552. 
§ Arch. ges. Physiol., 47, 454. 
| Virchow’s Archiv., 121, 501. 
_ ¥ Arch. ges. Physiol., 50, 98. 
