POISONS. 235 



I shall conclucle all I have to say upon the subject 

 of poisons by stating the interesting fact, that if 

 any of the narcotic or anfiesthesiating 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.* 



Tlie 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, fuithest 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 conductincr 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 throngh the opposite furrows, it was allowed to soak in 

 the poison while freely fit ating, and so without suffering pressui-e 

 in any of its parts. 



