6 PRACTICAL BACTERIOLOGY 



5. The Bacilli multiply by a process of division, which is transverse 

 to their direction of growth. The mother cell, having become elon- 

 gated, develops into two daughter cells in this way chains of indi- 

 viduals are formed. The length of these chains vary in the different 

 species, and is also influenced by different conditions. Long chains of 

 individuals, when this division is not very distinct, may present a 

 homogenous, thread-like appearance in unstained specimens. The 

 rapidity of the growth is naturally variable, according to the species, 

 nature of the medium, temperature, etc. The most rapid growth 

 observed has been the division of a mother-cell into two daughter- 

 cells within fifteen to twenty minutes. 



SPORE FORMATION. 



Some bacteria develop what are known as spores; by spores we 

 understand a resting stage in the life-history of an organism. Spores 

 are either formed within the mother-cells (endogenous), or certain 

 individual cells prove more resistant. Endogenous spores are formed 

 in the body of the bacilli, usually under conditions unfavourable to 

 their growth, that is, when they have exhausted their food supply : 

 this is, however, not alw r ays the case. Spores are usually resistant, at 

 times highly so, to influences which destroy vegetative forms. They 

 withstand drying, at times for many years, and great elevations of 

 temperature, as well as the effect of chemical agents. Brought under 

 favourable conditions the spores germinate again to the vegetative 

 form or bacillus ; they do not as such multiply of themselves, but give 

 rise each to a single bacillus which, dividing, gives rise to a definite 

 number of individuals. 



The changes in bacilli about to form spores are as follows : 



1 . The protoplasm loses its normal homogenous appearance, and 



granular refractive points of irregular shape and size 

 appear. 



2. The above granular refractive points finally coalesce, the 



remainder of the cell remaining clear and transparent. 

 Free granules may remain in the vicinity of the spore, as 

 if not required for its development. 



3. The complete spore appears as an oval, highly refractive, glis- 



tening body, easily differentiated from the remainder of 

 the cell, which now consists only of cell membrane and 

 detritus. 



4. The cell membrane eventually disappears, liberating the 



spore. 



