374 GEIfEEAL HISTORY OF THE INFUSORIA. 



of Leuk, at a temperature of about 80° ; and Ehrenberg heated water gradu- 

 ally to 120° Fabr., when Colpoda Cucidlus and Cliilodon Cuculhdus survived. 



Necessity of Air. — The water which Ciliata inhabit must be duly aerated 

 to support their existence, as is shown by the experiment of pouring a layer 

 of oil on the top of a vessel of water containing them, and by their disap- 

 pearance from a bottle which has been kept too long corked. 



They decrease in number and variety after water has been kept for some 

 time in the house, even though it remains sweet ; this is probably due in part 

 to the more stagnant atmosphere and the consequent diminished admixtui'e 

 of air with the water. 



Chemical Agents. Electricity and Galvanism. — Eor chemical substances 

 to act, they must be soluble in the water. Sea -water is generally more or 

 less speedily fatal to fresh-water species ; and, on the other hand, fresh 

 water is destructive to marine species, especially when the change of medium 

 is sudden. However, some species are common both in sea- and in spring- 

 water ; and there are others hving in brackish water which can readily ac- 

 commodate themselves to a change of habitation. 



There are also substances, such as sugar, which, although not in them- 

 selves poisonous, are damaging to animalcules, probably by causing an in- 

 jurious alteration in the density of the water. Other substances, having 

 active properties as poisons to animal life at large, such as corrosive subli- 

 mate, strychnine, arsenic, and the like, are also poisonous to animalcules. 

 Reference has been made to several chemical compounds which, by reacting 

 variously on the tissues of animalcules, are employed for the purpose of 

 demonstrating points in their organization: such are acetic acid, alcohol, 

 tincture of iodine, solution of potassa, &c. The last acts as a solvent, caus- 

 ing diffluence, as Mi\ Addison pointed out some years since (A. iV. H. 1843, 

 xii. p. 101). 



Of the effects of electricity, galvanism, and magnetism, we know little : ex- 

 periments with these forces are few and imperfect. Ehrenberg collected the 

 accoimts of several, among which are the following : — A shock from a Leyden- 

 jar charged with twenty sparks from an electrophorus having a resinous plate 

 7-|- inches square, and a collector 5^ inches, suddenly killed Stentor niger, 

 St. aureus, and AnipJiilejptus moniliger. The bodies of Ojyliryoglena atra and 

 Stentor polymorphus were entii^ely dissipated by it, as were also those of 

 Epistglis flavicans, after having first been thi'own from theii' stalks. It 

 generally requii'ed two such shocks to kill the Paramecium Aurelia. When 

 the electrical current passed near and not through them, their movements ap- 

 peared unsteady. Electricity slowly produced has a more powerful effect than 

 in the form of rapid shocks ; and when either it or the magnetic current de- 

 composes the water in which the animalcules are, then death is a necessary 

 consequence. 



Mr. Eood {Bill. Journ. 1853, xv. p. 71) has experimented more recently, 

 and states that, when a feeble galvanic ciuTent is passed through water con- 

 taining Paramecia, the animals are brought to a stand-still, particularly in 

 the neighbourhood of the negative pole, and after revohdng for a time on 

 their own centres, entirely cease to move ; ciliaiy action is also arrested, and 

 diffluence quickly ensues. 



On the subject of the operation of chemical reagents on Protozoa, or, strictly 

 speaking, on Paramecia, v^ith which he chiefly experimented, Mr. Rood has 

 the following remarks : — Alcohol stopped their motion, coagulated their con- 

 tents so that they shrunk within their integument, and caused speedy death. 

 Phosphate of soda killed in a few minutes ; and Epsom salts, the ammonio- 

 chloride of mercurv, acetate of lead, and perchloride of mercury destroyed 



