GENERAL REMARKS CONCLUSION. 85 



XVI. 



GENERAL REMARKS ON THE INFUSORIA. 

 CONCLUSION. 



THE Infusoria, like animals of higher organisation, 

 suffer and perish from sudden transitions of tem- 

 perature. They die in ice ; but, when the water first 

 congeals, each animalcule is surrounded by a moist 

 space, caused by the caloric liberated from its own 

 body *. . A high temperature also destroys them : Vor- 

 ticellaB often die under the microscope, if exhibited in 

 a hot room. Atmospheric air is as necessary for the 

 Infusoria, as for the warm-blooded animals. They are 

 killed by substances which affect the chemical composi- 

 tion of the water ; but the strongest poisons, if only in 

 mechanical suspension in the fluid, exert no influence 

 upon them. Fresh-water species instantly die if sea- 

 water be suddenly added, though the latter may swarm 

 with marine species ; but they survive if the mixture 

 be gradual, and many kinds inhabit brackish waters. 



* Ehrenberg. 



