INFUSORIAL ANIMALCULES. 31 



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. Dr. E. 

 states, that they exist much longer in an atmosphere of 

 nitrogen than in carbonic acid or hydrogen. The vapour 

 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 Infusoria can accommodate 

 themselves to different fluids, provided that the transition 

 be not too sudden. Thus, similar species may be found 

 in rivers, at their source, where the water is perfectly 

 fresh, and at their very mouths or junction with the salt 

 water of the ocean. Hydatinea have been fed ujDon 

 powdered rhubarb without being sensibly affected by it ; 

 nor does calomel or corrosive sublimate kill them ; at 

 least they live some time after these have been mixed with 

 the water. Strvchnia causes instant death. 



Section VIII. — Effects of Electricity, Galva7iism, and 

 Magnetism, on Infusoria. 



All the experiments on record, which have been made 

 upon animalcules with these powerful agents, appear to 

 me to have been conducted without a due regard having 

 been paid to their diminutive size ; and hence, as might 

 be expected, the results have proved fatal to their exis- 

 tence. We have, therefore, yet to learn what effects 



