INFUSORIAL ANIMALCULES. 23 



existed, on one occasion, in ^\'ater at 200*^ of Fall. If the increase 

 of temperature be sudden, the animalcules die at 140'^, notwith- 

 standing it be kept up for only half a minute. 



Some animalcules, however, discover an appropriate habital in hot 

 springs, and to such, consequently, we may suppose a high tempera- 

 tiu'e necessary. 



M. Doyere, by numerous experiments made with Rotatoria, Tardi- 

 grada, and AnguiUulce, has proved that those animals when put into 

 hot water at 212" Fah. were killed outright, but they retained the 

 power of re^-ival, when the water was at llS'^to 118°. When dried, 

 individuals were subjected to a heat of 216'', 252°, and even 261°, 

 some were found which were capable of being revived. 



Some Vilriones, which Focke discovered in milk, when frozen and 

 again thawed, continued to live, and even when they had been dried 

 for three weeks, revived on being moistened. 



Focke has mentioned that Pandorina morum, and other probosci- 

 dated monads, appear to change very much in colour according to 

 temperature and season. (See Reports Zoology : Ray Society, 1841). 



Section VI. — Effects of Air, Chemical Mixtures, and Poisons on 

 Infusoria. — That animalcules, Uke eveiy other part of the animal 

 creation, continually require fresh supplies of atmospheric au- for 

 their support, may be deduced from a variety of experiments. If a 

 thin pellicle of oil be spread over the sirfface of the water in which 

 they are contained, they very soon die from exhaustion ; and, indeed, 

 it must have often hajipened to those who are in the habit of col- 

 lecting Infusoria, that when the cork has been left, by accident, too 

 long in a phial full of water, they have experienced tliis mishap. 

 This is especially the case with respect to the large Rotatoria : 

 whenever experiments have been made with these creatures under 

 an exhausted receiver, the result has invariably been that vitality 

 ceases soon after the air has been expelled. Ehrenberg states, that 

 they exist much longer in an atmosphere of nitrogen than in carbonic 

 acid or hydi'ogcn. The vapoiu' of sulphur soon puts a period to their 

 existence. 



Poisons, which only mix mechanically with water, do not appear 

 to affect them materially, but those which are soluble, or combine 

 chemically with it, speedily destroy their lives. Many of the Infa- 



