PAUL F. CLARK 43 



Bacillus vulgatus 

 Bacillus mycoidcs 

 Mycobacteriaceae 

 Mycobacterium leprae 

 Mycobacterium smegmatis 

 Mycobacterium phlci 



Coryncbacterium diphthcriae 4 



Corynebacterium hofmanii 

 Coryncbacterium xerosis 

 Corynebacterium hodgkinii 

 PJeiferella mallei 



Henrici' studied in detail Vibrio comma, Escherichia coli, Bacillus megatherium. 

 Bacillus cohaerens, and an unidentified member of Corynebacterium. 



The increase in size during the "youth" of the cultures occurs in all the organisms 

 studied except the Corynebacteria and B. mallei. In these bacilli, more especially in 

 the first named, exactly the opposite progression occurs; the individuals from the 

 younger cultures (two to six hours) are the smallest, averaging in C. diphtheriae less 

 than half the size of the rods from a twenty-four-hour culture. The minimum size is 

 reached during the period of rapid reproduction ; during the phase of slow growth the 

 size increases, reaching the maximum during the resting period. As the individual or- 

 ganisms become smaller, the metachromatic granules disappear and the bacteria stain 

 uniformly and deeply with Loffier's methylene blue. Not infrequently at this stage 

 members of this genus form coccoidal chains. The peculiar pleomorphism, irregular 

 staining, and metachromatic bars and granules, so characteristic of the diphtheria 

 group, reappear as the cells increase in size again. 



The method employed in these studies hardly needs further description save to 

 add that Henrici' developed an admirable adaptation of the negative staining method 

 of Benians^ to distinguish between the living and dead bacteria in smears. This made 

 it possible to correlate precisely the changes in morphology with the rapidity of cell 

 division in the bacterial cultures. 



Members of the colon-typhoid group will serve as a basis for the more detailed con- 

 sideration of the typical mode of progression. A large majority of the bacteria in 

 a four-hour culture of B. typhosus are 4-6 micra long and 0.7-0.8 micron wide, so 

 large that they resemble the vegetative cells of the common spore-formers rather than 

 the usual picture of B. typhosus based on the examination of twenty-four-hour growth. 

 The increase in size is greater in length than in breadth, so that the larger cells are 

 relatively more slender. Chain formation occurs commonly at this stage even in those 

 species which in older cultures are characterized by discrete organisms. The bacteria 

 stain more intensely, and the outline is more sharply defined. The time when the 

 maximum average size occurs varies somewhat in different strains of the same or re- 

 lated species. This is dependent largely upon the duration of the period of "lag," 

 which according to Chesney^ is an expression of injury to the bacterial cell. By plot- 



' Henrici, A. T.: see various works cited previously. 

 'Benians, T. H. C: Brit. M.J., 2, 722. 1916. 

 3 Chesney, A. M.: /. Exper. Med., 24, 387. 1916. 



