44 Dr. D. F. Harris. On the Occurrence of — [Feb, 15, 
theless the time-relations of this tremor are comparable with those of the 
post-tetanic tremor of the higher muscular types. 
Crustacean muscle is no exception to the universality of this phenomenon 
of slow tremor appearing in muscles subjected to “tetanising” stimuli; i 
possesses, InN common with mammalian, avian, and amphibian oe 
protoplasm, that property of functional insusceptibility in virtue of which it 
avoids exhaustion by falling into a state of comparatively slow “rhythmic ” 
contractions. 
Part JJ.—ANALYSIS OF RESULTS AND THEORETICAL. 
(1) The first point that may be noticed here is that the tremor of post- 
tetanic onset is in its average periodicity not that of the tremor of the same 
muscle about to pass from incomplete to complete tetanus. H.g., in frog’s 
gastrocnemius the maximal rhythm of the incomplete tetanus (just before 
fusion to complete) is something between 25 and 28 per second,* while the 
“rhythm” of the tremor that follows spontaneously on a period of complete 
tetanus is about four to six a second. Instead of 25 to 28 responses per 
second, the muscle can now exhibit no more than five to six, or about one-fifth 
of the former. 
Obviously, fatigue is the cause of this physiological insusceptibility ; fatigue 
which, by preventing responses at anything like the rhythm of the stimuli 
(30 to 100 per second), prevents the early onset of complete exhaustion. This 
physiological insusceptibility may be taken as a protective mechanism against 
the fatal effects of full fatigue. 
(2) The post-tetanic tremor is a myogenic phenomenon. It occurs in 
muscle directly stimulated, whether curarised or not, and a tremor indistin- 
guishable from it is given by, eg., the dying diaphragm (fig. 10). For tremors 
of directly stimulated muscles, see figs. 28 and 3. For tremor of curarised 
muscle (toad), see fig. 9. 
The so-called “spontaneous” tremor I was able to record for three quarters 
of an hour in the dying diaphragm of a pithed rabbit which had its phrenics 
cut. It is a tremor of about six per second average periodicity and, therefore, 
quite similar in time-relations to the post-tetanic.t 
(3) While the periodicity of the post-tetanic tremor is rarely, during long 
periods, more than six per second, it is not of the same periodicity in all the 
muscles even of the same animal. 
* T. G. Brodie, ‘Elements of Experimental Physiology, pp. 62, 63. London: 
Longmans, Green, and Co., 1898. 
+ D. F. Harris, “On the Time-relations of the Spontaneous Tremor of the Diaphragm,” 
‘Phys. Soc. Proc.,’ January 26, 1907. 
