EXPERIMENTS IN STIMULATION. 53 



tlon 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-w^ater 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- 

 i:>eated, 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 

 wdll 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 induction shocks of the same 

 intensity, thrown in at three seconds' intervals — 



