152 On fhe Genetics of the Ciliate Protozoa 



reached the same conclusion. [Cf. Joukowsky (1898), Popoff (1908), 

 Rautmann (1909), Woodruff and Baitsell (191 U), Sun (1912), etc.] 

 The higher the temperature, the more rapid the rate of fission. For 

 example, Popoff (1908) found that Stylonychia niytilus divides about 

 once every 8 hours at 25° C, every 16 hours at 18° C, every 30 hours 

 at 14° C, every 48 hours at 10° C. Woodruff and Baitsell (19116), 

 Sun (1912) and Jollos (1913) point out that the increase in the rate 

 of division with increase of temperature follows van't Hoff's rule for the 

 velocity of a chemical reaction. 



56. There is, of course, a maximal and a minimal temperature 

 beyond which a ciliate cannot live and divide. These limits were 

 determined by Rautmann (1909) for Puramecimn as 35° C' and 5°C. 

 respectively. More recently Hutchison (1913), who has studied several 

 forms, concludes that each species " has a resistance jDeculiarly its own," 

 but " the amount of variation within the species may be considerable." 

 Different strains of Paramecium caudatwm, foi' instance, showed very 

 different powers of thermal resistance. 



57. Rate of fission may also depend to some extent upon the form 

 of nutrition (§ 19). An illustration of this is given by Joukowsky 

 (1898) who found that Pleurotricha reproduced more rapidly when 

 fed carnivorously on Uroiiema thari when kept in infusions of hay, 

 flour, or albumin. 



58. It was found by McClendon (1909) that the rate of fission in 

 Paramecium is accelerated if the animal is subjected to centrifugal 

 force for a certain time. His controls, however, seem to have been 

 abnormally slow in dividing, and the mortality excessively high. 



59. According to Peters (1904) KCl not only accelerates division 

 in Stentor (§ 52) but also modifies its character. The organism under- 

 goes an abnormal process of " budding " often forming very minute 

 " dwarfs." Further information about this curious phenomenon is to 

 be desired. The tlwarfs seem to have originated by what may be 

 called "chemical vivisection " or mutilation of the individual. It would 

 be interesting to know whether they are viable and able to reproduce — 

 whether they reorganize to normal size and form — whether they produce 

 dwarf or normal offspring. 



60. According to Joukowsky (1898) the size of a ciliate may depend 

 upon its food. Pleitrotricha was found to vary from 200 /j. to ]5 /x in 



' It was found that a temperature as high as 45^ C. might be withstood if the animals 

 were exposed to it for only a very short time. Compare also Jollos (1913). 



