588 Lorande Loss Woodruff. 



The Infusoria were handled with a pipet drawn out to a fine point. 

 Each pipet was used for one purpose and only one. All of the 

 Infusoria employed are of sufficient size to be seen readily with a 

 lens having a magnification of about ten diameters, and as it is 

 far more easy to operate with this than with a compound micro- 

 scope, it was used almost entirely in transferring specimens with 

 the pipet from one slide to another. 



At first hay-infusion was employed as a culture-medium, but 

 later it was found that an infusion of fresh grass gave equally good 

 results and had the advantage that one kind of grass could be 

 selected and used to the exclusion of all others, thus securing a 

 more uniform culture-medium. The infusions were prepared as 

 follows: About three grams of grass or hay was washed in tap- 

 water and then placed in a beaker containing about 200 cc. of 

 tap-water; this was boiled for one minute. In most cases this 

 infusion was used shortly after it had cooled but occasionally it 

 was allowed to stand for twenty-four hours. Except at certain 

 periods of physiological depression and during certain experiments, 

 to be described, this type of culture-medium was used throughout 

 the work. 



As pointed out by Biitschli and Calkins, Maupas's method was 

 inaccurate in that he assumed the rate of division of all individuals 

 of a culture to be the same and allowed a large number of speci- 

 mens to accumulate before computing the number of bipartitions. 

 Protozoa, like all other animals, have their individual physiolog- 

 ical peculiarities, as is shown by my own and similar experiments. 

 In order to obviate this source of error as far as possible and to 

 exclude the possibility of endogamous conjugation occurring in 

 the direct line of the culture, one individual from each line of 

 the culture was isolated almost every day. In the great majority 

 of cases not more than four individuals, representing two genera- 

 tions, were present at the time of transference. At each isolation 

 the single infusorian was put in fresh culture medium, the 

 remainder being kept as a reserve, or "stock," in case, through 

 accident or otherwise, the individual isolated did not live. 



Following the earlier workers, the maximum and minimum tem- 

 perature of the laboratory in the vicinity of the cultures, as 

 recorded by a registering thermometer, was noted daily. This 

 is, of course, but a rough method as the temperature within the 

 moist chambers is more constant than in the room itself; still, it 



