EXPERIMENTS IN STIMULATION. 53 
tion in Aurelia aurita with accuracy. It must be 
stated at the outset, however, that this period is 
subject to great variations under certain varying 
conditions, so that we can only arrive at a just 
estimation of it by understanding the nature of the 
modifying causes. To take the simplest cause first, 
suppose that the paralyzed Aurelia has been left 
quiet for several minutes in sea-water at forty-five 
degrees, and that it is then stimulated by means of 
a single induction shock ; the responsive contrac- 
tion will be comparatively feeble with a very long 
period of latency, viz. five-eighths of a second. If 
another shock of the same intensity be thrown in 
as soon as the tissue has relaxed, a somewhat 
stronger contraction, with a somewhat shorter latent 
period, will be given. If the process is again re- 
peated, the response will be still more powerful, 
with a still shorter period of latency; and so on, 
perhaps, for eight or ten stages, when the maximum 
force of contraction of which the tissue is capable 
will have been attained, while the period of latency 
will have been reduced to its minimum. This 
period is three-eighths of a second, or, in some 
cases, slightly less. 
Now, we have here a remarkable series of pheno- 
mena, and as it is a series which never fails to occur 
under the conditions named, I append tracings to 
give a better idea of the very marked and striking 
character of the results. The first tracing (Fig. 2) 
is a record of the successive increments of the 
responses to successive irtduction shocks of the same 
intensity, thrown in at three seconds’ intervals— 
