42 Dr. D. F. Harris. On the Occurrence of — [Feb. 15, 
second which, becoming rhythmic, was maintained of singularly constant 
intensity. 
To investigate the post-tetanic tremor in the bird, I used the pigeon 
(pithed). The extensor of the toes was the muscle chosen: a cord from the 
tendon for the toe passed to a hinged lever weighted with 20 grammes quite 
close to theaxle. Direct stimulation was maintained for 20 minutes; portions 
of the tremor during this time are reproduced in fig. 5. The average — 
periodicity of the tremor is three to five a second. 
In the case of the muscles of the fish, in some experiments I used those of 
the tail of the plaice or “spotted flounder” (Plewronectes platessa), the fish 
being pithed. Considerable difficulty was encountered in fixing the very. 
soft-fibred muscles to the recorder. 
Using the hammer as interruptor, and direct stimulation, I obtained 
a tremor of about one per second, which could not, however, be maintained 
indefinitely ; fatigue seemed to supervene with considerable rapidity ; 
I found great difficulty in bringing out smooth complete tetanus at all: the 
tendency to tremor was present from the first. 
When we used the muscles that close the jaw we obtained a tremor of 
a very slow periodicity, a shortening lasting about 1 second and occurring at 
irregular intervals of 3, 4, 5, or 6 seconds each. : 
In the case of the lobster (Homarus vulgaris), we used one of the flexors 
of the abdominal somites. The preparation was fixed by clamping a portion 
of the carapace in muscle-forceps and attaching the fibres of the muscle to 
a horizontal lever with a weight (10 grammes) very near the axle. The 
stimulation was, of course, in all cases direct, fine wires being led from the 
short-circuiting key in the secondary circuit directly into the muscle 
substance. 
On submitting the muscle of the lobster to stimulation similar to that 
employed in most of the other types of muscle (viz., stimuli given by Neet’s 
hammer, with side-wire), I failed entirely to produce complete tetanus; in 
other words, the muscle fell into a state of tremor from the very beginning of 
the stimulation. 
This is very well seen in fig. 7, where, using a quite fresh flexor of 
abdominal somite, a violent tremor is elicited without any preliminary period 
of complete tetanus. 
The periodicity of this tremor in the first second was nine a second, but, as 
fatigue set in, it fell to three a second. 
Thus, although we cannot use the term “post-tetanic” of the tremor 
which appears in the muscle of the fish or of the lobster in consequence of 
stimulation by rapidly recurring (tetanic) stimuli (30 to 70 a second), never- 
