SEX IN BACTERIA— EVIDENCE FROAl MORPHOLOGY 3 3 



completely by the growing bud, which now assumes the appearance 

 of a round body, the so-called "large body" (Fig. 12). Figures 16 to 

 19 illustrate a fusion process in wliich the budlike structure appears 

 on one end of the pair of rods. In some cases, after a rod has divided, 

 the daughter cells fuse directly without bud formation to produce a 

 large body. In such instances it is clear that sister cells fuse. In the 

 other instances of fusion, the cells that fuse are already found touch- 

 ing end to end and it is impossible to determine whether these cells 

 represent daughter cells of a previous cell division or cells of different 

 origins. Cells that come in contact with each other as a result of 

 elongation or cro\^ ding during growth have never been seen to fuse. 

 It may be significant, however, that fusion through bud formation 

 has not been observed in known sister cells. 



Fusion of rods in P. vulgaris OX- 19 occurs very infrequently. 

 Numerous fields must usually be followed before a single case of cell 

 fusion is observed. The exact frequency with which it does occur is 

 unknown, because cell fusion can be detected only by direct micro- 

 scopic observation and only a relatively few rods can be observed in 

 each microscopic field examined. 



Large bodies in cultures of F. vulgaris OX- 19, however, are 

 fairly numerous. The majority of these forms arise not by fusion but 

 by the swelling or budding of single rods. The latter two methods of 

 large body formation are illustrated in Figs. 1 to 3 and 4 to 7. 



The behavior of nuclear material (chromatinic bodies) within 

 the large bodies formed by cell fusion on the one hand and by bud- 

 ding or swelling of a single rod on the other hand would be inter- 

 esting to determine with certainty. At the present time some informa- 

 tion is available. In actively growing cells the areas corresponding in 

 position to the chromatinic bodies appear lighter than the rest of the 

 cell with the dark-phase contrast microscope, the reverse being true 

 with bright-phase contrast (Tulasne, 1949a; Stempen, 1950). When 

 this information is used in the examination of living organisms, the 

 chromatinic material in large bodies arising by cell fusion appears to 

 be in a compact mass immediately after fusion is complete. In other 

 cases where the large bodies do not arise by fusion, the interior of 

 these forms is composed of indistinct light and dark areas. This find- 

 ing suggests that the chromatinic material does not occur in a com- 

 pact mass but is more scattered throughout the interior of the large 

 body. Actually, in impression smears of organisms which had been 



