REPRODUCTION 3 



Reproduction. Bacteria are asexual, and propagate 

 by fission. When a cell has attained the maximum size 

 for its species, it elongates, with constriction round its 

 middle, followed by a simple partition. Hence the family 

 name of Schizomycetes. Two young cells are thus formed 

 from the mother cell. This process may be repeated as 

 often as once in twenty minutes if conditions are favourable. 

 An increase in geometric progression is not consistently 

 maintained, however, owing to various checks on the 

 growth. While insufficient food, lack of moisture, and 

 other conditions, disallow unhampered multiplication, 

 the chief hindrance is the production of inhibitory sub- 

 stances by the vital activity of the bacteria themselves. 



When bacteria have occupied the same site in the body 

 or lived in the same culture for a long period, or conditions 

 for growth are otherwise unfavourable, abnormal shapes 

 and sizes are produced (involution forms). These gener- 

 ally take stain less readily, or else do not stain at all. 

 Other characters, such as pathogenicity or fermentation 

 power, are likely to diminish, and there is general evidence 

 of degeneracy. 



The cbcci do not always separate after fission; division 

 may occur in one plane with the formation of a chain 

 (streptococci}; in two planes, producing a cluster (staphy- 

 lococci); or in three planes, forming cubical bales (sarcina). 



Spore-formation is not common; it occurs most fre- 

 quently in bacilli and spirilla, and rarely in micrococci. 



Endogenous Spores. The protoplasm becomes granular, 

 and some of the granules coalesce to form a highly re- 

 fractile round or ovoid body enclosed in a tough membrane. 

 Spores exhibit very great resistance to heat, desiccation, 

 and chemical agents. They are thus able to preserve their 

 species through most disadvantageous circumstances. 

 When favourable conditions recur, the spore loses its 

 refractile appearance, elongates, and bursts its membrane 

 to extrude an organism which divides in the usual manner. 

 Only one spore is formed in a cell, so that this cannot be 

 regarded as a reproductive process. While in most cases 

 the diameter of the spore does not exceed that of the parent 

 organism, it may be greater, and will give a ' drumstick ' 

 appearance if terminal and round; or it may be swollen 

 and club-shaped (clostridium). The conditions determin- 

 ing the formation of spores are variable for different 



