) 



Dr. R. McDonnell on the Electrical Power of the Actinm. 309 



water, so as to leave no doubt that some very remarkable influence has 

 been exerted upon it. 



These observations are no doubt familiar to all who have studied 

 the habits of these animals ; for although the tadpole seems more 

 susceptible of the peculiar stimulus which the Actinia can com- 

 municate than most of those creatures which are ordinarily cast in 

 its way, yet the same occurrences take place with the small crus- 

 taceans, &c. which are abundant in sea-water. Indeed no very close 

 attention is necessary to perceive, that while on some occasions these 

 little animals may creep to and fro over the surface and among the 

 tentacles of the Actinia, at other times they are seized and killed with 

 the greatest promptitude. 



Tt remained to be determined what is the exact nature of the 

 power which the Actinia has been thus found to have under its con- 

 trol. If it seized its victim by a simple mechanical eifort, why 

 should the tadpole be so agitated for some time after having 

 escaped from its grasp? No peculiarly viscid secretion could be 

 detected on the tentacles, nor could any decided reaction be discerned 

 on their surface differing from the feebly alkaline condition of the 

 sea-water in which they were placed ; moreover, the power of the 

 Actinia seemed often to be exerted with too much promptness to be 

 compatible with the notion of the formation of a poisonous or sting- 

 ing fluid over its surface. 



On the hypothesis that it is an electrical power with which the 

 Actiniae are endowed, it is obvious that the existence of animal elec- 

 tricity in them ought to be experimentally demonstrable by its 

 physiological effects, inasmuch as these phaenomena are the most 

 striking which animal electricity is capable of producing in common 

 with other electricities derived from different sources. 



The following experiments, in which the frog's limb was used as 

 a galvanometer (the limb of this animal being, as is well known, an 

 instrument of extreme delicacy for this purpose), seem satisfactorily 

 to establish the fact that the common Actiniae of our shores are 

 gifted with electrical power. 



1st. Having prepared the lower limb of a lively frog after the 

 mode described by Matteucci, by stripping off the skin, dissecting 

 out the sciatic nerve from among the muscles of the thigh, and then 

 cutting off the thigh a little above the knee, so as to leave the nerve 

 uninjured and as long as possible, the limb was laid on a small 

 piece of glass, so that the nerve hung down over its edge. The 

 pendent nerve was lowered into the water and gently brought in 

 contact with the tentacles of an expanded Actinia. From the first or 

 the second, or even several, possibly no effect may result, but 

 arriving at last at one more vigorous than his neighbours, smart 

 muscular contractions follow as he grasps the nerve in his tentacles, 

 and the toes are thrown into active movement. 



2nd. The next experiment, although of precisely the same nature 

 as that first detailed, renders the effect produced on the muscles of 

 the frog's limb more striking. A large and lively frog is killed, the 

 skin is stripped off', and the viscera being removed, the body is cut 



