24 Chapter I 



fresh- water Euplotes to a life in artificial sea water containing 4 / of 

 sodium chloride. In Balbiani's experiments l the fresh- water Monads 

 (Menoidium incurvum and Chilomonas paramaeciuni) died very 

 quickly on the addition of % of this salt ; but when it was added in 

 small successive doses (0'05 per day), they readily became accustomed 

 to a concentration of 1 % In the encysted state the Protozoa are even 

 more resistant than in the active state to the different salts that may 

 be added to their normal culture medium. It is probable that the 

 wall of the cyst interferes with the penetration of these substances 

 into the endoplasm. If a small quantity of an aniline dye be added to 

 a fluid containing encysted Infusoria, it is seen that the cyst-membrane 

 becomes very intensely coloured but the body of the Infusorian 

 remains unstained. The membrane absorbs a large amount of 

 colouring matter, after which, being saturated, it ceases to take it 

 up ; but it does not allow the dye to penetrate into the endoplasm. 



Balbiani (loc. cit. p. 580), having compared the action of the salts 

 of sodium with that of the salts of potassium and lithium on In- 

 fusoria, comes to the conclusion that the injurious influence of these 

 substances can only be partially explained by osmotic phenomena. 

 In addition to these a purely chemical action must be invoked. He 

 bases his opinion on the fact that the isotonic solutions of the three 

 [27] salts acting on Infusoria of the same species and same origin exert 

 a different influence. The salts of potassium and of lithium act in a 

 much more energetic fashion than do the sodium salts. Consequently, 

 the Protozoa are able to adapt themselves progressively not only to 

 noxious influences of a physiological character but also to those of a 

 chemical nature. Thus Infusoria and Rhizopods can be accustomed to 

 the action of high temperatures, to an intense light, etc. On the other 

 hand they can also be habituated to the toxic actions of true poisons. 

 Davenport and Neal 2 have established the fact that Stentors kept for 

 two days in a weak solution of corrosive sublimate (0'00005 / ) acquire 

 a tolerance to a dose of this poison four times as great as the lethal 

 dose for individuals previously kept in pure water. The same thing 

 has been observed in connection with the toxic action of quinine. 

 This immunity cannot be attributed to the selection and persistence 

 of those Infusoria which possess a natural resistance to the sublimate. 



1 "Action des sels sur les infusoires," Arch. cFanat. microsc., Paris, 1898, t. n, 

 p. 595. 



2 " On the acclimatisation of organisms to poisonous chemical substances," Arch, 

 f. Entwickdungsmech., Leipzig, 1895, Bd. n, S. 564. 



