226 ANIMAL PARASITES. 



2. The sensation which is thus produced by touch, not only 

 reminds one of the oscillations perceived by the eye when 

 coagulated jelly is set in motion, but by the percussion of 

 coagulated gelatine inclosed in glass, the same kind of sensa- 

 tions, recognisable by the touch, are actually perceptible. We 

 may easily convince ourselves of this by filling a small glass 

 bottle (of about 5 SS — 3J) w itli gelatine dissolved in hot water, 

 such as is employed for microscopic preparations, leaving it to 

 set, and then tapping upon the outside of the bottle, laid hori- 

 zontally. By this means we shall easily perceive that this 

 trembling is not only recognisable by the eye, but also by the 

 touch, and further that, according as the bottle is or is not 

 closed with a cork, and according as more or less air is left in 

 the bottle above the gelatine, different degrees of trembling are 

 experienced. 



3. For the perception of such a sensation it is by no means 

 necessary that the individual cysts should come into collision (as 

 has hitherto been supposed) ; but this trembling may certainly be 

 produced by the circumstance that the walls of one or several 

 cysts tremble in themselves by percussion, and communicate this 

 motion to the nearest cysts, which are still in a quiescent state, 

 without touching them directly, and thus the addition of the 

 trembling of the whole of the cysts at last becomes perceptible in 

 our hand. Of this faculty of the animal walls of the Echinococci 

 every one may easily convince himself, when he is in possession 

 of daughter-vesicles of Echinococcus. If such vesicles be laid 

 upon a glass plate, they will continue to vibrate for a long time 

 after the application of a moderate force to the glass plate, even 

 when they have been long kept in alcohol. 



4. From this it follows also, that the cysts of Echinococcus 

 scolicipariens will exhibit no hydatid-trembling, but, at the utmost, 

 a simple fluctuation, because they contain no daughter-vesicles 

 capable of trembling. 



5. We also see at once that the hydatid-trembling can only 

 occur in colonies of E. altricipariens, and even here only under 

 certain favorable circumstances. First, a certain number of 

 daughter- vesicles, which must not be too small, so that the 

 quaking may communicate to several neighbouring vesicles, 

 and a greater action may be produced by addition. Second, a 

 certain consistence of the fluid surrounding the individual vesicles, 

 with regard to which, as appears from the laws of the trans- 



