EFFECTS OF ALCOHOL ON INFUSORL-^. 8/ 



it is believed that a satisfactory culture medium for comparative 

 work was obtained. When the isolated protozoon had divided 

 twice, producing four individuals, each was isolated on a separate 

 depression slide and thus were started the four lines of which each 

 culture consisted. Thus, for example, Paramecium, culture I, 

 comprised four lines, I-a, I-b, I-c and I-d. These lines were 

 thenceforth kept distinct unless one became extinct through the 

 isolation of a weak individual or through accident, in which case 

 the line was started again from one of the three surviving sister 

 lines of the same culture. 



The rate of division was recorded daily for each of the four 

 lines, and at the time of record an individual from each line was 

 isolated on a clean depression slide in five drops of hay infusion. 

 In computing the rate of division of the culture as a whole, with 

 which we are alone concerned, the four lines {a, b, c, d) of the 

 culture were averaged together and this result was again averaged 

 for five-day periods. By this method it is believed that a just 

 conception of the rate of division of the culture was obtained, as 

 the average of the four lines largely obliterated the fluctuations in 

 the division rate of any one line, which may not have been of 

 much significance, or which may have been merely due to the 

 isolation of a weak individual. One who has carried on cultures 

 of protozoa for considerable periods cannot fail to recognize the 

 fact that, as is to be expected, individuals vary greatly in their 

 general vitality, etc., and it is necessary to isolate representative 

 individuals. It is here that the personal equation of the experi- 

 menter comes into view, and therefore it is desirable that the same 

 person should make the daily isolations. 



The culture slides were arranged in small moist chambers to 

 prevent evaporation. As in previous experiments of this nature, 

 the minimum and maximum temperature of the room in the vicin- 

 ity of the cultures was recorded daily, as indicated by a reg- 

 istering thermometer. By averaging the minimum and maximum 

 points of each day for five-day periods the results obtained are 

 quite satisfactory for comparative work. In the experiments 

 under consideration, as in those of previous investigators in this 

 field, the rate of division was taken as the indication of the phys- 

 iological condition of the organisms ; it being generally accepted 



