30 GENERAL HISTORY OF 



in it, becomes frozen, and is placed under a microscope, 

 in a cold situation, Dr. Ehrenberg states that if the ice be 

 clear, each animalcule or group will evidently be sur- 

 rounded by an exceedingly small portion of water, which 

 that naturalist supposes to be occasioned by the superior 

 temperature or animal heat of the creatures preventing 

 congelation ; and he is of opinion, that in all cases where 

 this portion of the water freezes, the animalcule neces- 

 sarily dies. 



If the water containing polygastric Infusoria be gra- 

 dually raised to a temperature of even 125° of Fah. these 

 creatures will live ; and Dr. E. observes, that some of the 

 Chlamidomonas pulvisculus existed, on one occasion, in 

 water at 200^^ of Fah. If the increase of temperature be 

 sudden, the animalcules die at 140°, notwithstanding it 

 be kept up for only half a minute. 



Section VII. — Effects of Air, Chemical Mixtures, and 

 Poisons, on Infusoria. 



That animalcules, like every other part of the animal 

 creation, continually require fresh supplies of atmospheric 

 air for their support, may be deduced from a variety 

 of experiments. If a thin pellicle of oil be spread 

 over the surface of the water in which they are retained, 

 they very soon die from exhaustion ; and indeed, it must 

 have often happened to those who are in the habit of 

 collecting Infusoria, that when the cork has been left, by 

 accident, too long in a phial full of water, they have ex- 

 perienced this mishap. This is especially the case with 



