POISONS, 235 
I shall conclude all I have to say upon the subject 
of poisons by stating the interesting fact, that if 
any of the narcotic or anesthesiating agents be 
administered to any portion of a contractile strip 
cut from the umbrella of Aurelia aurita in the way 
already described, the rate of the contraction-waves 
is first progressively slowed, and eventually their 
passage is completely blocked at the line where the 
poisoned water begins. Upon now restoring the 
poisoned portion of the contractile strip to normal 
sea-water the blocking is gradually overcome, and 
eventually every trace of it disappears.* 
The contractile wave may be blocked by poisons 
in another way. A glance at Fig. 11 will show 
that a circumferential strip cut from the umbrella 
of Aurelia aurita is pervaded transversely by a 
number of nutrient tubes, which have all been cut 
through by the section. At the side of the strip, 
therefore, furthest from the margin there are situ- 
ated a number of open ends of these nutrient tubes. 
Now, on injecting any of the narcotic poisons into 
* In conducting this experiment, care must be taken not to exert 
the slightest pressure on any part of the strip. The method I 
adopted, therefore, was to have a vessel with a very deep furrow 
on each of its opposite lips. Upon filling this vessel to the level 
of these furrows with the poisoned water, and then immersing 
the whole vessel in ordinary sea-water up to the level of its brim, 
some of the poisoned water of course passed through the open 
furrows. The external body of water (i.e. the normal sea-water 
containing the animal) was therefore made proportionally very 
large, so that the slight escape of poison into it did not affect 
the experiment. On now passing the portion of the strip to be 
poisoned through the opposite furrows, it was allowed to soak in 
the poison while freely floating, and so without suffering pressure 
in any of its parts. ; 
