50 Dr. D. F. Harris. On the Occurrence of — [Feb. 15, 
the post-tetanic (three or four to six a second), and as the coarse tremor 
brought on by fatigue in, eg., the human deltoid (fig. 19). 
Fic. 19.—Deltoid, human, coarse fatigue tremor of. Arm held out horizontally with 
1 kilo. in hand; cord from middle finger to button of cardiograph (Marey’s). 
Tracing by a recording tambour. Time in half-seconds. Periodicity of tremor, 
5 per second. To be read from left to right. (Facsimile.) 
In these cases we may say that inco-ordination of fibres or of fasciculi is 
the element common to all, whether this has been brought about by “non- 
simultaneous innervation ” or by repeatedly varying degrees of the excitability 
of the fibres brought on either by fatigue or by some hitherto unexplained 
state of inaccessibility to certain stimuli. 
I take it that this inco-ordination or non-simultaneousness of innervation 
is what Dr. Haycraft alludes to when, discussing normal voluntary tetanus, he 
writes . . . “ muscles exhibit fascicular or other local movements.”* 
If this be true as regards normal voluntary tetanus, the record of which 
is very regular compared with the tremors under study at present, it must 
apply with increased force to those tremors of muscles in which fatigue has 
set in. 
While fatigue, inducing fascicular inco-ordination, can be held to explain 
the irregularity of the post-tetanic tremor and the spontaneous tremors of 
dying muscle, it is difficult to see how fatigue can be the main factor 
producing the irregularity of such tremors as those from chemical, mechanical, 
or thermal stimulation or from anelectrotonus, seeing that the irregular 
contractions are present from the very first when fatigue obviously cannot 
have set in. 
The probability is that those stimuli called “ single ” or “ constant” are, as 
regards nerve-molecules, anything but constant in their stimulating power. 
* J. B. Haycraft, “Voluntary and Reflex Muscular Contraction,” ‘Phys. Journ.,’ 
vol. 11, 1890, p. 366. 
