38 Dr. D. F. Harris. On the Occurrence of —[Feb. 15, 
the frog’s gastrocnemius is four to six a second, can be maintained unaltered 
as to its time-relations, but of slowly declining amplitude, for a relatively long 
time (half an hour). 
Fig. 1 shows the smooth line of complete tetanus, breaking off into the 
post-tetanic tremor in the frog’s gastrocnemius stimulated indirectly.* 
On investigating as many animal types as I could procure, I found that a 
post-tetanic tremor could be demonstrated in man, cat, kitten, rabbit, pigeon, 
and frog, both with and without intact circulation, the mean periodicity of the 
tremor in all types being between two and six or eight per second. 
An analogous tremor is elicitable in muscles of fish and lobster. 
Fig. 3 is a facsimile of the tracing obtained by stimulating the human 
flexor sublimis digitorum by rapid induction-shocks. 
After the time of complete tetanus is over, the muscle falls into a state of 
irregular tremor which in my own arm I caused to be maintained for half an 
hour, during which time it did not alter either in intensity or in average 
periodicity. 
Sponge-electrodes were placed on two spots, an upper and a lower, on the 
fore-arm over the flexor sublimis digitorum. The middle finger had a ring 
slipped over its terminal phalanx, and from this a thread passed over a pulley 
to the spring of an ergograph.t 
The interruptions here were 60 per second (380 makes and 30 breaks); and 
as there was previous independent evidence to show that the makes were 
subliminal, I may take it that 30 break shocks per second constituted the 
“ stimuli.” | 
The responses occurred with an average periodicity of four per second. The 
ratio of stimuli to responses is then 30:4 or 7°5:1, 7e., 1 in 7°5 may be said 
to be the figure of physiological insusceptibility in this case. Obviously the 
muscle had its circulation intact. 
[I may say that at the end of half an hour I experienced no sensation of 
fatigue in the muscle, but in the above and in all similar experiments on my 
own muscles the sensations of “the muscular sense ” were quite distinct. A 
thrill corresponding to the rate of stimulation was perceptible. ] 
The next type of muscle I investigated was that in the cat. In one 
experiment, a young cat was pithed under a dose of A.C.E. mixture and 
artificial respiration done. The Tendo Achillis was fastened to a bell-crank 
lever, a 50-gramme weight being attached as near the axle as possible. 
Direct stimulation of a muscle with intact circulation was kept up for 
* The current in the primary circuit that was usually employed for tetanic stimulation 
was one of about 3°8 amperes (voltage 4:2). 
t+ The “ period ” of this spring was 40 to 42 per second. 
