THE BACTERIAL NUCLEUS 73 



remove of two nuclear divisions, with or without cell division, in the case of 

 the fusion-fragmentation method ot reproduction. While the truth of this 

 interpretation cannot be established with certainty until technical methods 

 permit the accurate identification of individual chromosomes, or else enable 

 the process of nuclear division to be followed in the living cell, it is certain 

 that the appearance of fixed and stained material, at different stages of the 

 process, does not encourage any other interpretation. It may be argued that 

 this method of study is unreliable, but it was until recently the only method 

 by which the nuclear processes accompanying cell division could be studied 

 in all types of cell ; these processes have recently been examined by the 

 technique of phase-contrast cinematography, with the result that the earlier 

 interpretations have in most respects been most admirably verified. But the 

 most remarkable vindication of the now classical observations of bacterial 

 cytology is the manner in which genetical work has, quite independently, 

 confirmed every conclusion after a greater or lesser delay. 



A complete distribution of nuclear material, on the lines of mitosis in 

 higher types of organism, could only occur if it were possible tor the halves 

 of the newly-divided chromosomes to slip past one another and occupy a 

 position in the opposite half of the dividing cell. Not only is there no evidence 

 that this may occur, except the rather doubtful figures of crossed chromosomes 

 referred to previously, but the genetical evidence entirely supports the concept 

 of a reductional chromosome division. Supposed classical mitotic figures, 

 which have been claimed to be demonstrated in bacteria cannot be taken 

 seriously. 



It follows, therefore, that although bacteria may commence their lite, in 

 a particular culture, with a set of two or four chromosomes oi different genetic 

 constitution, possibly derived from the sexual processes which appear to 

 precede the formation of the resting nucleus, these differently constituted 

 chromosomes will rapidly become segregated, without the intervention of 

 further sexual conjugation. It appears that the vegetative generations of 

 bacteria of this type are haploid, but sometimes multinucleate, a conclusion 

 which is borne out by genetic studies (Chapter X). The multinucleate 

 condition is irregular, bacteria in the same culture may have one, two, four 

 'or more chromosome-like nuclei. 



