BACTERIA 7 



for the most part separate at once ; occasionally, however, they 

 are found adhering in pairs (diplobacilli) or chains (streptobacilli). 

 Certain spirilla show a tendency to remain attached. Thus when 

 seen through the microscope a single cell of one of the shorter 

 forms may have the appearance of a comma, a pair the letter S, 



FIG. 1. Cocci, Bacilli, and Spirilla. 



and the union of several elements may appear as a long spiral 

 form (Fig. 1). 



Under favorable conditions cell division takes place very rapidly. 

 A cell may reach maturity and divide in from twenty to thirty 

 minutes. It has been estimated that if bacterial multiplication 

 continued unchecked for two days and the division of each cell 

 took place only once an hour the descendants of a single cell would 

 number 281,500,000. It has been further calculated that these 

 281,500,000 bacteria would form a solid pint and would weigh 

 about a pound. Such multiplication, however, does not actually 

 take place. Bacterial growth may be checked by various factors, 

 such, for example, as unsuitable temperature, lack of food and 

 moisture, the disintegration of food substances into various injuri- 

 ous products such as acids and alkalies, the excretion of the bac- 

 teria, or the competition of other organisms. 



Involution Forms. When the bacterial environment has 

 become unfavorable to growth the bacteria may show extremely 

 irregular structures quite different to the ,-, (== ^ > 

 original forms. Long thread-like organisms ft A O ^^ s? 

 with irregular thickenings may develop which ^ Q^ 



assume a dumb-bell or flask-like shape (Fig. Fio- 2. involution 

 2). These are termed involution or degenerate 

 forms. That they really represent degenerate changes is shown 

 by the fact that when transferred to favorable conditions growth 

 slowly takes place into typical forms again. It sometimes hap- 

 pens, however, that these involution forms lose certain properties 

 which are never regained. 



