EFFECTS OF A DIET OF RICE ON PARAMECIUM. 55 



equal amount of fresh water and 5 c.c. of fresh malted milk were 

 added. 



In order to eliminate as far as possible the influence of unknown 

 variables every effort was made to prevent contamination of 

 the culture media; graded pipettes were used in measuring the 

 media and the slides containing the individuals were kept in a 

 moist chamber at constant temperature, and removed for ob- 

 servation at approximately the same hour every day. Individuals 

 for the special problem were isolated on March 9, 1918, three 

 being taken from each pure line. Of these three, one was isolated 

 on a depression slide in two drops of distilled water and two drops 

 of i per cent, rice water made from polished rice, and a third in 

 two drops of distilled water and two drops of I per cent, rice 

 water made from unpolished rice. The rice water was prepared 

 by boiling .5 gram of finely ground rice in distilled water and 

 making up the solution to I per cent, after evaporation. The 

 number of divisions was noted at the end of every twenty-four 

 hours, and one individual from each group was isolated on a 

 clean slide in the same medium as before. While the bacterial 

 content is a questionable factor in the experiments, it is con- 

 trolled to a large extent by the sterilization of slides and pipettes, 

 by the boiling of all media and by the daily isolation of the indi- 

 viduals in fresh media. 



Some trial experiments were made for perfection of technique, 

 and then, using eleven days as a fair unit of time, final averages 

 were made of the rates of division in each group. The indivi- 

 duals in malted milk showed the normal rate of division which 

 was slightly higher than that in hay infusion. Peebles (8) has 

 shown that if rightly used a weak solution of malted milk is a 

 most satisfactory culture medium. The metabolic activities 

 of the individuals in polished and in unpolished rice exhibited 

 the influence, not only of the presence and absence of the vita- 

 min, but also of the change of environmental conditions as repre- 

 sented by a new culture medium. Results are given in the 

 accompanying tables. 



The number of divisions during the first twenty-four hours of 

 experimentation are not given in the tables, because some time 

 must be allowed for adaptation to new conditions. 



