1907.]  Post-tetanie Tremor in Several Types of Muscle. 51 
Drying of nerve in air, abstraction of water by NaCl, increase of temperature, 
even pinching the nerve cannot be assumed to be respectively uniform 
in their modes of being stimuli; in fact, physically they represent stimuli 
varying considerably in intensity from moment to moment. They introduce 
intra-molecular disturbances of various potentials and of varying disruptive 
powers as regards the biogens of the nerve. These disturbances “act” like 
discrete stimuli of varying intensities. 
Theoretical Explanation of the Meaning of the Post-tetanic Tremor* and 
Tremors of Similar Perrodicity. 
The property of functional inertia of muscular protoplasm expressed here 
as a physiological insusceptibility to certain stimuli seems to me to furnish 
the key to the meaning of the post-tetanic tremor. I regard it as a 
protective mechanism which, by permitting the establishment of this 
fatigue-rhythm of low periodicity, averts for a time the physiological calamity 
of full exhaustion. 
If there could be responses to such high rates of stimulation as 30, 40, or 
100 per second, the muscle would very soon be utterly tired out and 
incapacitated for a long time from activity. But, owing to the possession 
of the property of physiological irresponsiveness (functional inertia), the 
muscle subjected to continued stimulation responds only to some of the 
stimuli in the rapid series (every fifth, seventh, or tenth), or responds at a 
rhythm very much lower than that of the stimuli, thus substituting chronic 
fatigue for acute exhaustion. 
Here, in virtue of functional inertia, the living matter preserves itself 
from that destruction which would overtake it were it possessed of 
affectability alone. The two properties are co-existent in the living matter: 
resting muscle has much affectability, but little functional inertia; as 
activity proceeds, the affectability diminishes and the functional inertia 
Increases towards the continued stimulation, until a point is at last 
reached when the ratio between the two properties is such that only every 
1 in 7 or 10 stimuli is responded to, the others being functionally 
disregarded. This state of matters can be exhibited for a long time, 
biologically speaking, viz., half an hour, as in the post-tetanic tremor of Ene 
human flexor sublimis digitorum with intact circulation. 
The biotonic state at any moment depends on the ratio of the degrees of 
possession of these two properties; were affectability alone present we 
* D. F. Harris, “Functional Inertia, a Property of Protoplasm,” ‘Roy. Soc. Edin. 
Proc.,’ vol. 24, p. 196; and D. F. Harris, “ Affectability and Functional Inertia as the two 
Properties of Protoplasm,” ‘Scot. Micros. Soc. Proc.,’ vol. 4. 
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