52 Post-tetanic Tremor in Several Types of Muscle. 
would have, as a result of perfect response to all stimuli, a maximum 
uncontrollable activity, and the rapid end of things in death; were 
functional inertia alone present, we would have complete irresponsiveness to 
all stimuli. 
But a condition of functional compromise between the two biotonic extremes 
is set up, and thus a mean condition, known as “ fatigue,” established. 
I take the existence of the post-tetanic tremor as one more expression of the 
physiological significance of fatigue and of rhythm. 
In those tremors arising from a single stimulus (figs. 15, 16, and 17), or 
from continued stimulation (figs. 13 and 14), or spontaneously (fig. 10), we 
have the property of functional inertia of the muscular substance con- 
tributing to the explanation of the feature common to them all, the want of 
correspondence between the character of the responses and the nature and 
mode of application of the stimuli. 
Tremors of the same average periodicity, 3 to 6 a second, are elicited 
by stimuli physico-chemically the most varied, and may be seen charac- 
terising cases so far apart physiologically as the dying diaphragm and the 
maximal rate of beat of the heart ventricle. 
_ This non-correspondence or lack of parallelism between stimulation and 
response seems to be due to the stimulus-disregarding property of functional 
inertia in the muscle-substance, the same property which, in the case of 
Iong-continued rhythmic stimulation, expresses itself in the post-tetanic 
tremor. 
Through affectability muscle responds to any stimulus by contracting, but 
through functional inertia the nature, the mode of application, and even the 
rhythm of the stimulation is disregarded, and to the most varied kinds 
of stimulation the response becomes the same—a tremor whose component 
events recur with the same slow average periodicity. 
“Tt seems,” writes Professor Biedermann,* “to be an almost universal 
property of muscular substance to fall, under certain conditions, with all 
prolonged stimuli into a state of visible rhythmical excitation.” The above 
data, I submit, are an experimental and statistical verification of this 
statement. 
[The expenses involved in the foregoing work have been met by a grant 
from the Carnegie Trust for the Universities of Scotland, of which I here 
desire to express my grateful acknowledgment. | 
* ¢Klectro-physiology,’ vol. 1, p. 107. London: Macmillan, 1896. 
