THE MORPHOLOGY OF BACTERIA 9 



3. THE ARRANGEMENT OF BACTERIA 



Bacteria may occur singly or be aggregated into groups. A 

 unilateral arrangement of individual cells is called a chain. 

 Chains of cocci are called streptococci, Fig. 4, o; chains of ba- 

 cilli, streptobacilli, Fig. 4, n; and chains of spirals, streptospi- 

 rilli. Fig. 4, /. Bacteria may be arranged in twos. Thus cocci 

 in twos are diplococci, and bacilli in twos diplobacilli. 



Cocci in irregular groups are designated as staphylococci, Fig. 

 4, q ; in fours as tetracocci ; in larger rectangular plates as meris- 

 mopedia; and in cubical packets as sarcina. Fig. 4, w. 



4. THE VEGETATING GROWTH OF BACTERIA 



In the ordinary vegetative growth of bacteria multiplication is 

 by fission. The exact process of cell division for the bacteria 

 is not known, but is probably similar to that of the lower fila- 

 mentous algae, as illus- 

 trated by Strasburger 

 in Cladophora, Fig. 5. 

 Here, as seen at («), a 

 narrow ring of cellulose 

 forms upon the cell wall, 

 which gradually extends 

 inward until it closes 

 in the centre, a process 

 which is nearly com- 

 pleted at (J}). Bacteria 

 multiply in geometric ra- 

 tio, and under optimum 



conditions of temperature and nutrition a single cell of B. sub- 

 tilis will divide in 30 minutes, and of the cholera Microspira in 20 

 minutes. At this rate a single cholera organism will in 24 hours 

 produce a billion trillion individuals. In certain coccoid and rod- 

 shaped bacteria division may take place in only one direction 



Fig. s.- 



- Showing cell division in Cladophora fracta 

 after Strasburger. 



