432 LORANDE LOSS WOODRUFF AND RH. ERDMANN 



II. MATERIAL AND METHODS 

 A, METHODS OF CONDUCTION OF THE MAIN CULTURE I 



Since the results presented in the present paper are based on 

 a cytological study of the main pedigreed race (I) which has 

 been carried on for the past seven years, a brief outhne of the 

 methods employed in its conduction must be given. For further 

 details the reader is referred to earlier papers on this race (Wood- 

 ruff '08, '11). 



A specimen of Paramaecium aurelia was isolated from a labo- 

 ratory aquarium on May 1, 1907, and placed n about five drops 

 of hay infusion on an ordinary glass slide having a central de- 

 pression. When the animal had divided twice, producing four 

 individuals, each of these was isolated in fresh media on a sepa- 

 rate slide, thus forming the four main hnes (la, lb, Ic, Id) of 

 this culture, Paramaecium aurelia I. This pedigreed race has 

 been maintained by the isolation of a specimen from each of the 

 four Unes practically every day during the more than seven 

 years of its existence. The isolations have been made with a 

 capillary pipet and a Zeiss binocular microscope, oculars 2, ob- 

 jectives 55a. This daily isolation has prevented the possibility 

 of conjugation occurring, afforded fresh culture medium, and 

 enabled an accurate record of the generations to be kept. There- 

 fore this is a pedigreed culture of Paramaecium. The rate of 

 division of the culture has been determined by averaging the 

 daily rate of these four lines and the accompanying graphs show 

 this again averaged for various periods as indicated in the respec- 

 tive legends (text fig. 2). 



The culture material supplied to the main lines of the race 

 has consisted of thoroughly boiled infusions of materials taken 

 practically at random from ponds, swamps, etc., in an endeavor 

 to supply the general type of material ordinarily met with by 

 this organism in nature. The depression slides holding the ani- 

 mals have been kept in a glass moist chamber on a laboratory 

 table and therefore the organisms have been subjected to the 

 ordinary fluctuations of temperature, light, etc., of the room. 

 The morphological condition of the animals has been followed 



