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 began. This time, as 
already stated, was slightly 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 during which a continuous flood of light 
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 represent the time during which light requires to act 
before it becomes an adequate stimulus? 
