64 LECTURE in. 



to freeze some Infusoria in a watch-glass, and examined the clear ice 

 in a cold room : he observed that those which appeared to be frozen 

 and imbedded in the mass were actually inclosed in very minute 

 vesicles in the ice. He conceives that they may remain torpid in this 

 state through the winter, and revive when their little ice-houses have 

 been melted away in spring. 



Infusoi'ia are destroyed generally by expanding and bursting, after 

 a few minutes' subjection to the heat of boiling water. 



In water subjected to a galvanic current strong enough to cause 

 decomposition, the contained Infusoria are killed. When subjected to 

 a weaker current, those only which came into its course were affected : 

 some Rotifera were observed to be stunned only, and afterwards 

 recovered ; others were killed. 



Tenacity of life is a very striking physiological character of the 

 Infusoria. 



The famous phenomena of the revival of Rotifera, after having 

 been completely dried and apparently killed, certainly when reduced 

 to the state of the most complete torpidity, were first observed by 

 Leeuwenhoek in the year 1701.* The father of microscopical anatomy 

 had been engaged in examining some specimens of Rotifer vulgaris 

 with Euglena sanguinea, and had left the water in which they were 

 contained, to evaporate. Two days afterwards, having added some 

 rain-water, which he had previously boiled, within half an hour he 

 saw a hundred of the Rotifera revived and moving about. A similar 

 experiment was followed with the same result after a period of five 

 months, during which period the Rotifera had remained in a state of 

 complete desiccation and torpidity. These observations wei*e repeated 

 by Hill f and Baker.^ You will find all the experiments that were 

 recorded before the time of Haller accurately quoted in his great 

 *' Physiologia Corporis Humani," vol. viii. p. 111. Fontana § kept 

 Rotifera two years and a half in dry sand, exposed to all the power 

 of an Italian summer's sun : yet in two hours after the application of 

 rain-water they recovered life and motion. Goze, Corti, and Miiller 

 recorded similar experiments : but those performed by the celebrated 

 Abbe Spallanzani are perhaps most generally known. He succeeded 

 in reviving his Rotifers after four years' torpidity : he alternately 

 dried and moistened the same animalcules twelve times with similar 

 results, except that the- number of the revivers was successively 

 smaller ; after the sixteenth moistening he failed to restore any of 

 them to life. \\ 



* XXXIX. p. 386. t XL. p. 11. 



I XLI. Chapters iv. and vi. § XLIL torn. i. p. 87. 



II XLIir. vol. ii. p. 127. 



