EXPERIMENTS IN STIMULATION. 45 



interesting question, because if such a lengthened 

 period of latent stimulation occurs in this case, it 

 would stand in curious antithesis to the very short 

 period of latent stimulation manifested by the con- 

 tractile tissues of the same animal under other 

 modes of irritation. To test these alternative hypo- 

 theses, I employed the very simple method of first 

 allowing a continuous flood of light to fall suddenly 

 on the Medusa, and then noting the time at which 

 the responsive spasm first bi'gan. This time, as 

 already stated, was slightty more than one second. 

 I next allowed the animal to remain for a few 

 minutes in the dark to recover shock, and, lastly, 

 proceeded to throw in single flashes of light of 

 measured duration. I found that unless the flash 

 of light was of slightly more than one second in 

 its duration, no response was given ; that is to 

 say, the minimal duration of a flash required to 

 produce a responsive spasm was just the same as 

 the time durino^ which a continuous flood of lioht 

 required to operate in order to produce a similar 

 spasm. From this, therefore, I conclude that the 

 enormously long period of latent excitation in 

 response to luminous stimuli was not, properly 

 speaking, a period of latent excitation at all ; but 

 that it represented the time during which a certain 

 summation of stimulating influence was taking 

 place in the ganglia, which required somewhat more 



represent the time during which the series of physiological pro- 

 cesses are taking place in response to an adequate stimulus, or 

 does it rejiresent tlie time during which light requires to act 

 before it becomes an adequate stimulaa ? 



