64 THE CYTOLOGY AND LIFE-HISTORY OF BACTERIA 



short rods. And in fact they occasionally appear as though viewed troni the 

 end, although not so frequently as might be expected in such a case. The 

 figures of Robinow and Kliencberger-Nobel occasionally show the pairs 

 of rods crossed. In the experience of the author this is exceedingly uncommon, 

 but if the chromosomes are in fact rods there is no theoretical reason why 

 they should not appear crossed. Genetical evidence also supports this concept 

 of a reductionally dividing nucleus (Witkin, 195 1). 



The slightly dumbbell-shaped appearance of the chromosomes is usual, 

 although not invariable. It is not indicative of division in the transverse 

 plane, as might, perhaps, be expected. Division of the chromosomes is 

 invariably by longitudinal splitting, and it is obvious that if these bodies 

 carry the genes of the cell, arranged in a linear manner, as from genetical 

 considerations must necessarily be true, then their division cannot take place 

 hi any other way. 



The nuclear unit of the vegetative cell is a single pair of chromosomes. 

 In bacteria of unicellular, smooth morphology a pair is disposed at each end 

 of the cell, but it is probable that both pairs are of identical genetical con- 

 stitution (Chapter X). In very young cultures of bacteria of this morphology 

 the cells often contain only a single pair of chromosomes, and the bacteria 

 mav contain from one to four or six cells (Chapter III). Each of the four 

 cells of a rough bacillus contains one pair of chromosomes, but the arrange- 

 ment of the cells, and the method of cell division in the two, morphological 

 types, are perfectly distinct (Chapter III). It is probable that these multicellular 

 smooth bacteria occur mainly in cultures which are in process of 

 germination. 



D: GERMINATION OF THE RESTING STAGE 



(27, 30, 31, 32, 3S, 36, 39, 55, 61) 



The germinaticMi of the spore, microcyst or resting cell is accomphshed 

 ill exactly the same manner in each case. The cell commences to elongate, 

 and in the case of some spores and microcysts, casts the outside wall. The 

 vesicular nucleus is transformed into a single, large transverse rod, which 

 almost immediately divides into two, and afterwards, in the case of smooth 

 types, into four. Normal cell division then commences. 



