FAST AND SLOW RECORDS OF FATIGUE 
203 
EXPERIMENTAL 
The mechanism to this end (Plate I), aside from the custom- 
ary relative adjustments and positions of the various parts, is in 
its essential details rather simple and is adapted to any laboratory 
with little trouble. A muscle lever of the Harvard type is pro- 
vided with two aluminum rods instead of one. These are curved 
away from their support in such a way that their distal ends each 
form an arc of a quadrant. Thus their writing tips may be 
brought into contact with their respective drums. By slight ad- 
justments both points can be made to rub lightly upon the drums 
which by previous preliminary trials have been fixed to rotate at 
definite relative speeds. The fast type, in records soon to be dis- 
cussed, was set for one revolution in four seconds, while the slow 
type was made to revolve once in an hour. The muscle received 
its successive stimuli by the automatic contact interrupter mounted 
upon the fast drum housing. By the use of this mechanism, com- 
parable records are obtained in which it is possible to follow ex- 
cursion after excursion of the writing points throughout the en- 
tire .fatigue process. By mounting signal magnets and chrono- 
meter in proper position checks on time of stimulation and rela- 
tive duration of any phase or groups of phases can be made and 
subsequently analyzed. By count of actual excursions of the 
lever or by interposing simple signal devices any response can be 
located at will, thus, for example, in typical records B and B', the 
one, two or three hundredth responses are located definitely on 
each curve. 
In attempting to analyze fatigue curves by either method, one 
is forcefully impressed with the fact that there are characteris- 
tically at least two types to be found, and possibly inter-grada- 
tions which when analyzed resemble in certain of their features 
one or the other of these. One of these extremes is illustrated 
by curve G and the other curve by A' in Plate II. Among the 
chief points of difference in these, obviously, are differences in 
first and secondary contracture, and primary relaxation, the form- 
er exhibiting all three phases to a marked degree, the latter com- 
paratively lacking them all. Why this should be is a matter of 
interesting speculation. From the physiological standpoint the 
phenomenon of contracture, when compared with that of a simple 
contraction indicates the possibility that two different contraction 
processes may take place in an irritable muscle, one involving 
the so-called state of tone and therefore the length and hardness 
of the muscle at all times, the other concerned with the actual 
