RFPUODUCTION 97 



unknown in human strains of M. tiihcmilosis, but seldom results in the forma- 

 tion of structures more complex than a Y-shaped bacillus. A " branchinjr " 

 strain ot C. diphtherial examined by the author, appeared perfectly normal 

 and unbranched except in very yoimg cultures, where, by ordinary staining 

 methods, a picture was produced, suggestive of extremely profuse branching. 

 When stained by cell wall stains, however, the appearance was of masses of 

 adherent bacilli, and occasional, small, lateral excrescences or buds in the cell 

 wall. These buds developed, most frequently, in positions where the normal 

 growth of the cells was obstructed by the adhesion of neighbouring bacteria. 

 They were probably no more than outgrowths of cells unable to increase in 

 size by elongation, in the ordinary manner. 



It is o( some importance that the defuiition of branching, as a taxonomic 

 character, should under no circumstances be based upon heat-fixed. Gram- 

 stained material, nor, preferably, upon the evidence of smears. Whenever 

 possible, whole mounts of colonies should be used, stained by an appropriate 

 cytological technique. It is of interest to note that whereas several workers 

 have described StreptohaciUus moniliformis as a branched organism, upon the 

 evidence of heat-fixed smears, van Rooyen (1936) showed, by means of 

 impression colony preparations (Chapter II), that branching does not occur. 

 The very frequent use of the epithet " tangled," in qualification of the des- 

 criptive term " mycelium " is an adequate commentary upon the disinclination 

 of research workers to differentiate between the natural effects which they 

 wish to study, and the artefacts which inevitably arise from the mishandling 

 of biological material. 



G ; S UMMA R Y 



The lag phase of the growth cycle corresponds to the period of germination 

 of the microcyst, the logarithmic phase, to the period of nuclear activity, and 

 in the decline phase the resting condition of the nucleus is adopted. The 

 nucleotide content of the cell is correlated with these changes in nuclear 

 activity. 



Vegetative reproduction may be asexual or sexual, simple or complex. 

 ^Analogous methods of fragmentation and regeneration occur in eubacteria 



