The Physiology of Nematocysts 369 



Mechanical Pressure 



The effect of mechanical distorting pressure was studied by 

 mixing the nematocysts of Physaha or the tentacles of Metridium 

 with granulated salt and grinding the material between glass 

 plates. Sometimes the salt was omitted, and ground glass plates 

 were used. After treatment in this manner, the nematocysts were 

 examined. In those cases in which salt was used, this was dis- 

 solved before observations on the results of the treatment could be 

 attempted. In this way a considerable mechanical distorting 

 pressure was applied to the individual capsules, and though the 

 nematocysts of Metridium, on account of their minute size and 

 their delicacy, gave inconclusive results, those of Physalia gave 

 very positive ones. Many partial discharges were obtained. 

 Pressure on the cover glass of a preparation of Physalia nettles 

 also causes many partial discharges. Such pressure as was used 

 in these experiments distorts the capsules, and is effective because 

 the internal pressure of the nematocysts is raised by distortion. 



Uniform External Pressure 



That the effects of distorting pressure have been correctly inter- 

 preted, is clearly shown by the effect of high uniform external 

 pressure. Such pressure was applied by allowing the nemato- 

 cysts to be drawn up into a capillary tube provided at one end 

 with a reservoir filled with mercury. The open end of the tube 

 was then sealed and the mercury made to expand. 



The pressure obtained in this manner, calculated from the con- 

 traction of the air bubble inside the tube, and from the bursting 

 strength of the tube, was from 50 to 100 atmospheres. No nemat- 

 ocysts ever discharged when treated in this way. 



Solutions 



In Table II are presented in condensed form the results of 

 experiments undertaken to discover the effects on isolated nemat- 

 ocysts of the same solutions which had previously been employed 

 on the living tentacles and acontia of Metridium. The isolated 



