108 A MANUAL OF BACTERIOLOGY 



bend and straighten themselves, etc. At other times 

 the motile microbes become motionless. In this 

 state many of them aggregate together and excrete 

 a gelatinous material which entirely envelopes them. 

 This colony is termed a zoogloea, in fact it is the 

 resting stage of the particular microbes. In the 

 zooglcean stage, microbes often produce spores. 



Microbes multiply by fission (i.e. division) and 

 spore-formation. The warmer the air, etc., the 

 faster proceeds the division, and the stronger the 

 multiplication ; in a lower temperature it becomes 

 slower, and ceases entirely at the freezing-point of 

 water. Their fecundity is enormous, and would, in 

 a very short time, choke up the earth ; but this 

 rapid rate of increase is kept in check by the 

 limited supply of food, climatic conditions, and the 

 struggle for existence. 



As an example of the enormous fecundity of mic- 

 robes we describe the rate of reproduction of a 

 common form, viz., Bacillus sultilis. This bacillus 

 attains a certain length and then divides across into 

 two. 'Each half grows to the size of the parent, 

 and then similarly divides, and so on as long as 

 food and other conditions of their life are present. 

 Bacillus sultilis has been observed to divide in this 

 way every half-hour, a rate which gives in twenty- 

 four hours more than three hundred billion of in- 

 dividual microbes as the offspring of one parent. 

 They are extremely minute, varying from 20 ^ ^th 

 of an inch to the TzyWth of an inch in length.' 



As already stated, microbes propagate by fission 

 and by spore-formation. The following table gives 



