Bauhaus-Universität Weimar

Plethysmographic and Vaso-Motor Experiments with Frogs [From the Journal of Physiology, Vol. VI, No. 6, Offprint]
Ellis, Fred W.
the tendency to contraction increases with the number of 
induction shocks per second. For example, in one case we may 
have an intensity of 150, a duration of 10" and a rate of one shock 
per second. In a second case we may suppose the intensity to he 10, 
the duration to he 10" and the number of shocks per second to be 15. 
The total stimulation in both cases is the same, but, in the first instance 
we might have dilatation, and in the second contraction. 
The effect of the induction shocks is cumulative. The stimulus 
imparted by the induction shock is practically instantaneous, but its 
effect abides for an appreciable length of time, and gradually subsides. 
If a second shock is received before the effect of the first is completely 
worn away, and then another shock at an equal interval of time, and so 
on, the effect of the stimulus will go on increasing up to a certain point. 
Hence, a single induction shock, or a limited number of such shocks, 
which alone are not of sufficient intensity to produce any effect on the 
blood-vessels, may be able to do so, if they are repeated in a sufficient 
length of time. 
It would be idle to assume that the effect of a powerful shock wears 
away as quickly as that of a weak one, but we are not justified in 
assuming that the length of time during which the effect of such a 
stimulus persists is directly proportional to the intensity of the shock. 
It is very possible that a weak shock may produce a greater proportional 
disturbance in the nerve than a strong one. No doubt a portion of the 
electrical energy of the shock is converted into some form of molecular 
disturbance in the nerve ; but we have no reason to assume that the 
amount of energy thus appropriated is always in exact ratio to the 
intensity of the shock. Hence, it appears probable that in two cases 
where the total stimulation is the same, the irritation may be greater 
with rapidly interrupted weak shocks, than with shocks of greater 
intensity following one another at greater intervals. 
As the susceptibility of different frogs to shocks of varying intensity 
and frequency varies, so may that of the same frog under different, con¬ 
It is evident that the apparatus and methods used in these investi¬ 
gations can be profitably employed in studying many problems in vaso¬ 
motor physiology that remain to be investigated. 
The plates are exact photographic reproductions of tracings. The 
size of the tracings was reduced one-ninth to accommodate them to the 
size of the page. Much of the delicacy and sharpness of the original 
tracings is lost in the reproductions, which are in other respects perfectly


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