43 
tractions take place. Secondly, during the intervals, however 
short, the proteid residues will be able to gather more kations, 
though fewer as time goes on, because the supplies get used 
up ; nevertheless they will be able to do so to some extent all 
the time, and this corresponds to the fact that in tetanus the 
muscle is really vibrating-, though its vibrations are imper- 
ceptible by ordinary methods.* This is further confirmed by 
che fact that too rapid a succession of stimuli corresponds in 
effect to a persistent stimulus, even in striated muscles. f 
Schoenlein & Richet's observations of ''rhythmically interrup- 
ted tetanus" in striated ijiuscles are doubtless due to the 
hyaloplasm reclaiming kations from the spongioplasm at the 
point of stimulation during the intervals. | Another reason 
for the rapidly decreasing height of the summated stimuli lies 
in the fact that the elastic re-action of the walls of the sar- 
cous elements becomes less and less as the muscle contracts, 
so that each new contraction in the series starts with less force 
to counteract the pull of the surface tension than the pre- 
vious one ; hence absolute tetanus may correspond to a state 
of the sarcous elements in which no pull is being exerted on 
the wall at all. That ''fatigue" is really due to the diffusion 
of the kations into the spongioplasm is shown by the fact that 
in the ureter ''each wave of contraction produces a temporary 
depression of excitability and conductivity in the sheet of 
muscle, from which it only recovers during the subsequent 
diastole and interval (just as in the striated muscle-nets of 
insect intestine)." § This also illustrates the rapidity with 
which the hyaloplasm recovers itself and again gathers 
kations : one is also reminded of the "refractory period" in 
the heart. It may be frequently observed that when a frog's 
gastrocnemius has been tetanised through its nerve for as long 
as several minutes, so that the lever has almost dropped to 
the base line again through fatigue, if the tetanising current 
be opened only for a moment, and then closed again, the 
muscle, if it is fresh, will contract in tetanus almost to the 
same height as before. We should, indeed, expect that 
striated muscle with its low /8 (and consequently high sensi- 
bility), and a comparatively large surface of spongioplasm to 
regain kations from, would have a very much shorter "re- 
fractory period" than the heart or the smooth muscle of the 
ureter. 
* Bi-edermann : Electro-piiysiology: Trans, by F. A. Welby. 
vol. i., page 135. 
t Ihld., vol. i.. page 131. 
ij: Ihid.. vol. i., page 131. 
§ Ihid., vol. i., page 167. 
