124 GARY X. CALKINS 



Encystment tests 



Encystment, with its accompanying asexual reorganization^ 

 has never occurred in my isolation culture dishes. It does occur, 

 however, at certain periods of the life cycle in the Syracuse dishes 

 during the conjugation tests. Once encysted, the organism can- 

 not be coaxed out until after a longer or shorter period in a dried 

 state. Such encystments are particularly abundant just prior 

 to the first epidemic of conjugation in a series, and, in some tests, 

 practically all of the individuals encyst without conjugation. In 

 such cases the S\Tacuse dishes are set aside and the culture 

 medium is allowed to evaporate. Such Syracuse dishes with the 

 dried cysts are then stacked away for future experiments. After 

 several weeks or months of storage, fresh cultm-e medium is 

 added to the Syracuse dish containing the dried cysts. In some 

 cases the reorganized individuals emerge by the end of a week; 

 in others, two or three weeks may be required. Series B and M 

 were derived from such encj^sted indi\dduals. The cytology of 

 reorganization during encystment will form the subject of a later 

 paper. 



The measure of vitality 



Reproduction by division is an indication that cell structures 

 are functioning normally, and the rate of division is an index of 

 the condition of metaboUc acti\dties of the protoplasm, or a 

 numerical index of the protoplasmic vitality of a series for a given 

 period. The relative activity of a given protoplasm at different 

 periods or of parent and offspring protoplasm for the same period 

 may be obtained by averaging the number of divisions per day 

 in a series for successive periods of the same length of time, e.g., 

 five days, ten days, or sixty days. If we compute the average 

 division rates in this way for successive ten-day periods from 

 start to finish of a series and plot the results, we obtain a curve 

 indicating the relative vitahty of the protoplasm of a series at 

 different periods throughout the life cycle. Furthermore, since 

 all series and all lines are fed daily at the same time and with the 

 same standardized culture medium, if we plot a number of curves 

 representing different series which have originated at different. 



