EFFECT OF FOOD ON GROWTH OF PARAMECIUM CAUDATUM. 83 



the contents of the cells to enter the solution. One potato 

 solution was boiled and strained, the other was strained raw. 

 The controls were maintained in .2 per cent, solution malted 

 milk. It was customary to feed the control and experimental 

 lines an equal quantity of freshly made solutions every other day. 

 The same food pipette was always used. Isolating pipettes 

 were sterilized in boiling water each time used to avoid con- 

 tamination in change of food and to kill any Paramecia that 

 might have remained in the pipette. Such sterilization is not 

 sufficient to destroy bacteria. All Paramecia were kept in 

 depression slides in a moist chamber at constant temperature. 



I. EXPERIMENTS WITH FOOD HORMONES. 



The following tables show the number of divisions in several 

 control and experimental lines. This experiment was carried on 

 for twelve days and a record kept of each da'ly division. The 

 table shows the data averaged in periods of six days each. 

 Varying proportions of food substances were used. Although 

 the total quantity of food was always the same in both lines, 

 one set of experiments contained two drops of raw potato solution 

 and one drop of the basic food substance malted milk with a 

 control of three drops of malted milk; and another three 

 drops of raw potato solution with a control of four drops malted 

 milk. 



TABLE I. 



POTATO (RAW). Daily Division Average For Six Day Periods. 



With raw potato the average rate of growth in the weaker 

 solution was practically the same as that of the control while 

 the rate of division for the stronger extract exceeded that of the 

 control. 



