400 Pedigreed Race of ParamcEciiim [Mar. 



weak extract of beef as a constant culture medium.^ Further, beef 

 extract should afford all the Clements required for the continued 

 life of protoplasm. From a series of preliminary tests it was 

 found that a Solution of approximately 0.025 per cent. of Liebig's 

 extract of beef gave the best results and accordingly a quantity of 

 this Solution was made up which was sufficient to provide culture 

 medium for the organisms for a long period. The medium was 

 put into over one hundred test tubes and these were plugged with 

 cotton and sterilized, The Solution in the various tubes remained 

 sterile until used, and the inoculation of the medium with bacteria 

 which were transferred with the paramsecia afforded an ample 

 supply of food for the animals. 



The regulär experiment was begun by isolating from the main 

 culture at the 2,oi2th generation a sub-culture which was subjected 

 to a constant culture medium of beef extract. This sub-culture 

 flourished on the beef extract medium until this treatment was dis- 

 continued at the end of ten months. During this period the rate of 

 division of the "beef" culture was quite similar to that of the 

 "varied environment" culture and neither of the cultures showed 

 any indications of loss of vigor. The rate of division of each at 

 the end of the experiment was practically the same as at the begin- 

 ning — such fluctuations as occurred in the interval being merely 

 rhythms. It is evident, then, that the "constant" medium em- 

 ployed proved to be practically as favorable a medium for the 

 reproduction of this strain of Paramcecium as the "varied environ- 

 ment" medium, and therefore the conclusion seems justified that 

 this culture can, in all probability, be continued indefinitely on the 

 constant medium, It therefore appears that it is the composi- 

 tion of the medium rather than changes in the medium which 

 is conducive to the unlimited development of this culture without 

 conjugation or artificial Stimulation.'^ 



* Woodruff and Baitsell : The reproduction of Paramcscium aurelia in a 

 "constant" culture medium of beef extract. Journ. Exper. Zoology, vol. 11, 

 no. I, 1911. 



^ Cf. Woodruff : Evidence on the adaptation of paramsecia to different en- 

 vironments. Biol. Bull., vol. 22, no. i, 191 1. 



