DO 



2. CiHatr,^. CJrci'k'V (li»()l) ohscrvcd llial wiu-ii cul- 

 tures of Stent or coc rill CHS were cooled slowly, ciliary 

 movement continued for 1 to 3 liours at 0°, after which 

 the cilia and i>ullet were absorl)ed, the ectosarc was thrown 

 off, and the endosarc transformed into a spherical cyst- 

 like ('(,'11. When the tempeiature was again raised, these 

 resting cells underwent a reverse process, and resumed 

 their normal activity. If the temperature was lowered 

 rapidly and the culture medium was solidly frozen, the 

 organisms were killed. 



According to Efimotf (1924), Parawaeciuw can with- 

 stand freezing (Ausfrieren) at -1° for 30 minutes, but 

 is killed when frozen at the same temperature for 50 to 

 60 minutes. Various infusoria {Paramaecium caudatum, 

 Colpidium colpoda, Spirnsfomuni aml)ifjuum) die in less 

 than 30 minutes when exposed to temperatures below -4°. 

 Rapid and short subcooling (not l)elow -9°) produces no 

 injury, but, if it is prolonged, the paramaecia become 

 spherical and swell up, increasing their volume 4-5 fold, 

 while the other infusoria shrivel up and assume irregular 

 contours. 



To study the effect of low temperatures on Para- 

 maecium in a subcooled medium. Wolf son (1935) enclosed 

 these organisms singly or in numbers from 2 to 116 in 

 capillary tubes and observed them microscopically during 

 cooling in a specially constructed, metal, glass-bottomed 

 well, cooled by stout metal leads connected with a brass 

 plate on which pieces of dry ice were placed as desired. 

 Warming was effected by means of a heating coil wound 

 about these same conducting leads. He found that both 

 bodily and ciliary movements could be observed down to 

 - 14.2°. Then, all bodily movements ceased, but the cilia 

 continued to beat for some time yet. While organisms 

 subjected momentarily to -16° were found to recover 

 completely, after a longer cooling at that temperature 

 morphological degeneration set in, manifesting itself in a 

 rounding up of the oi'ganism, an apparent increase in cell 

 volume and a marked visibility of the nucleus, followed by 



