62 MORPHOLOGIC VARIATION 



pension was then placed on a cover glass, which was inverted over 

 a hanging drop slide and sealed with vaseline to prevent evaporation. 

 These were incubated in an electric warm stage at 30° C. With the 

 low-power lens a cell or small group of cells was found. This was then 

 focused upon with the oil immersion lens, and watched continuously 

 for some hours, the progress of events being recorded by camera 

 lucida drawings. Such micro-colony observations are not easily 

 made, for if the preparation is heavily seeded, so that the cells are 

 easy to find, then the growth rate is low and the morphologic varia- 

 tions are slight. If, however, the preparation is lightly seeded, so 

 that there are only a few cells in the whole preparation, then these 

 cells are difficult to find, and in such preparations isolated cells fre- 

 quently failed to grow for some hours. Many such preparations 

 were made and observed at intervals all day long, without any evi- 

 dence of growth being seen, and then on the following morning it 

 was found that a good sized colony had developed. Most successful 

 results were obtained when small groups of cells, generally in chains, 

 were found well isolated from any others. 



The results of such continuous observations of growing micro- 

 colonies are presented in Figures 10, 11, and 12. The first developed 

 from two cells, both of which commenced to grow shortly after the 

 observation was begun and grew at approximately the same rate 

 throughout the period of observation. Over three hours was re- 

 quired for the first cell division to take place. During this period, 

 however, the cells had greatly elongated, to considerably more than 

 twice their original length, and the contained granules had gathered 

 at the poles of the cell, and had perhaps also decreased somewhat 

 in number. After the first cell division, which occurred approximately 

 simultaneously in the two cells, the four resulting cells again increased 

 markedly before they divided, increasing once more to more than 

 twice the size at the preceding cell division. The second micro-colony 

 developed from three cells, of which only one grew, the other two 

 showing no changes in morphology during the period of observation. 

 The cell which grew showed its first evidence of growth in an in- 

 crease in length, with, at the same time, a decrease in the number of 

 granules and an accumalation of these granules at that end of the 

 cell which was not in contact with its sister cell. Cell division oc- 



