648 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
had achieved that object he had broken down, at any rate, temporarily. It was well 
known that in a 100-yards race the man who made the greatest effort, and put the 
greatest possible endurance into that effort, was practically absolutely exhausted, and 
this corresponded to the yielding of the metal specimen when it gave way. It was the 
same with the man who ran 100 miles, but he could only maintain a less speed for that 
distance; the same result was obtained with the breaking down of the metal under less 
stress when the reversal of stress was further prolonged, and there was every reason for 
both kinds of curves being logarithmic in form as they were. Thus, muscular fatigue 
corresponded in a certain way to the endurance tests of metals. 
It was only quite recently that physiologists had understood the reason of the limits 
of muscular endurance, which limit was reached because of the formation of the toxins 
MILES PER HOUR 
et a : 
Hpk 
jena 
salute 
pa 
MILES 
Fic. 7.—Fatigue curve of metals, compared with muscular fatigue, fig. 2. 
in the muscles, and which toxins must be dissipated and the muscle renewed. Thus, 
if a man made a certain effort, he could not renew the toxins sufficiently quickly to keep 
that effort going beyond a certain distance. In the case of metals was there anything 
similar comparable with that? In that connection he approached a subject that had 
already been alluded to by previous speakers, though not in such a way as to account 
for the results he had referred to. Scientists at the present time, did, however, know 
the reason, and had discovered an explanation of the extraordinarily puzzling phe- 
nomenon of fatigue of metals as well as of muscular fatigue. He had before him a proof 
copy of the most valuable and interesting lectures! that Dr. Rosenhain delivered 
1 Proceedings 1911, pt. 2, p. 241. 
