29 



SECTION II. PROTOZOA 



1. Bh'izopods. According to Kiihiic (1804), Amoeba 

 and Actinuphrys are killed when their culture medium 

 freezes, but they suffer no injury when they are kept at 

 0° for several hours, as long as the medium is not frozen. 



Molisch (1897) observed under the microscope Amoeba 

 freezing in drops of water. He found that the organisms 

 die as soon as the ice forms in their proximity or within 

 them, that is, at a temperature slightly below zero. 



Chambers and Hale (1932), who proceeded in a similar 

 manner, state that the internal freezing of Amoeba, which 

 they induced by inserting an ice-tipped pipette into the 

 interior of the organism, occurs at - 0.6°. Internal freez- 

 ing always kills these animals, while, if ice is not present 

 in them, temperatures as low as -5° produce no damage. 

 These authors describe how the ice spreads through the 

 protoplasm in the form of fine feathery crystals radiating 

 in all directions from the point touched by the pipette. 



According to Deschiens (1934), dysenteric Amoebae, in 

 the vegetative form, were destroyed in a short time when 

 their medium froze, at a temperature of - 5°. They could 

 be kept alive, though immotile, for 56 hours, at 0.0°, in the 

 unfrozen medium. 



Fol (1884) obtained growing Amoeba from dried earth 

 which he put to freeze in Pictet's apparatus at a tempera- 

 ture of about - 100°. 



Becquerel (1936) revived several species of rhizopods 

 from dried soil cooled to the lowest available tempera- 

 tures. He kept in a vacuum, with barium oxide, at 35°, 

 for 3 months, samples of soils containing various micro- 

 organisms. When the soils were thoroughly dried he 

 sealed one portion of them in glass tubes evacuated to 10~^ 

 mm. of mercury and placed another portion in glass tubes 

 closed with cotton plugs. Thereupon he subjected all the 

 tubes to liquid helium (-269° to -271°) for 7^ hours and 

 subsequently to liquid nitrogen (-190°) for 480 hours. 

 From both groups of soils he obtained, after this treat- 

 ment, living Amoeba proteus, Amoeba Umax, Amoeba 

 dacfylifera and Aci'mophrys sol. 



