590 Lorande Loss Woodruff. 



the general result. Throughout this work, as in that of my 

 predecessors, the rate of cell-division is taken as the indication of 

 the physiological status of the cultures; it being generally accepted 

 that this is a just criterion of metabolic activity. 



The experiments w^ere started in the Zoological Laboratory of 

 Columbia University, New York City, and carried on there con- 

 tinuously (except for a short period during the summer months) 

 during the first two years of the work. The last year of the work 

 was done at the Thompson Biological Laboratory of Williams 

 College, Williamstown, Massachusetts. 



III. DESCRIPTION OF THE CULTURES. 

 I. Oxytricha fallax, Culture A. 



On October 26, 1901, a specimen of Oxytricha fallax was found 

 in an aquarium, in the Columbia laboratory, containing water 

 and superficial slime taken a few weeks before from a stagnant 

 pond at Van Cortlandt Park, New York City. The individual 

 was isolated on a depression slide in a few drops of hay-infusion 

 as previously described. Two days later the infusorian having 

 divided twice, each of the four individuals was transferred to a 

 separate slide, thus starting the four lines of Culture A which are 

 designated respectively A-i, A-2, A-3, and A-4. The accom- 

 panying diagram shows the daily record of divisions of all four 

 lines averaged together and this again averaged for each ten-day 

 period of the life of the culture. 



As is indicated in the diagram, the culture started with an 

 average rate of a little over one division per day for the first 

 ten-day period. This was increased to one and three-quarters 

 divisions for the second ten-day period, after which there were two 

 periods in which the rate fell each time below that of the first 

 period, i. e., in period four to exactly one division per day.^ 



'From November 20 to 24, in the third period, A-i and A-2 were changed from the hay-infusion 

 to a medium of flour and water, prepared by boihng a pinch of flour in about 25 cc. of tap-water for 

 fifteen minutes. This was used about an hour after cooHng. This change of medium was made 

 because I became alarmed at the rapid fall in the division-rate — not having become acquainted, as yet, 

 with the general hfe-cycle of hypotrichous forms. That the use of the flour had no apparent efi^ect was 

 shown by a comparison with the division-rate of A-t, and A-4 which were continued on the hay-infusion 

 diet. I 



