INFUSORIAL ANIMALCULES. 23 



from 113 to 118 Fab. Some kinds, however, are extremely sensitive, and are 

 unable to endure an ordinary degree of warmth. This is the case with the Bell- 

 flower animalcule, which dies under examination in a hot room. Most of the 

 Polygastrica retain their vitality at temperatures considerably below the freezing 

 point; but when the mercury descends as far as 7 or 8 Fah., many species can 

 no longer exist. One kind of the Bell-flower animalcule still lives after being ex- 

 posed to a temperature of 8 Fah. and the ice then gradually thawed in which it 

 was frozen ; but not more than one individual in a hundred can survive this ordeal. 

 The Rotatorial animalcules are more susceptible, and perish when the cold is less 

 severe. 



During the Antartic expedition under Capt. James Ross, animalcules were found 

 existing in great abundance in those inclement regions. In the sediment obtained 

 from melted ice. floating in round masses, in the latitude of 70, more than fifty 

 species of loricated Infusoria were discovered alive, notwithstanding the extreme 

 cold to which they had been exposed. According to Dr. Ehrenberg, when a layer 

 of clear ice containing animalcules is examined under a low temperature by the 

 microscope, each animalcule or group will be seen surrounded by a very small 

 portion of water, which he supposes is prevented from freezing by the natural heat 

 of their bodies ; and he likewise believes that death inevitably ensues whenever 

 the cold is sufficiently intense to congeal this enclosing film of water. 



AIR. Air is as necessary to existence of Infusoria as to any other class of ani- 

 mated nature ; for when they are denied access to the atmosphere, and are thus 

 prevented from receiving constant supplies of pure air, life becomes extinct within 

 a short time. If oil is poured upon the water containing animalcules, and the sur- 

 face of the fluid is entirely covered with the oil, the air is necessarily excluded and 

 the creatures speedily die. Or should the naturalist fill a phial with water in which 

 animalcules reside, and leave it corked tightly for any length of time, he will have 

 the mortification of finding, on examination, that the fluid, once so full of life and 

 activity, has become entirely inert, and that millions of existences have passed 

 away. The fact that air is necessary to the existence of Infusoria has been parti- 

 cularly noticed in regard to the larger kinds of wheel-animals ; for when experi- 

 ments have been made by placing these creatures under the receiver of an air 

 pump, they have always ceased to live soon after the air has been withdrawn from 

 the vessel in which they were contained. 



Dr. Ehrenberg affirms, that if animalcules are placed in nitrogen gas they exist 

 for a longer time than if they are immersed in carbonic acid or hydrogen gas. In 

 the fumes of sulphur they quickly perish. 



POISONS. The most powerful poisons, which mingle simply in a mechanical man- 

 ner with water, like earth, do not affect the lives of animalcules placed in the 

 mixture ; but those which unite chemically, and are dissolved in the fluid, soon 

 deprive them of their existence. One kind of Infusoria has been known to live so 

 long in water with which calomel and corrosive sublimate had been mixed, that it 

 was doubtful whether their death was to be attributed to the effect of those in- 

 gredients or not. 



Many species of animalcules can adapt themselves to a gradual change in the 

 nature of the element in which they live, but a sudden transition kills them. For 



