28 BACTERIA 



The bacterium passes into the resting state and awaits more favorable 

 conditions. When these arrive, whether it be days or years later, the 

 spore passes into the vegetative form and reproduction and multipli- 

 cation begin anew. 



Multiplication. When bacteria reach a certain size, which is fairly 

 constant in the species, the cells divide. In bacilli and vibrios fission 

 occurs at right angles to the long axis. In cocci the cleavage may 

 occur in only one plane forming streptococci; in two planes forming 

 staphylococci ; or in three planes, forming sarcinae. The rapidity of 

 multiplication and growth to maturity varies with conditions. It has 

 been estimated that if fission occurs hourly without interruption, in 

 forty-eight hours the descendants of a single individual would number 

 more than 200,000,000. However, such a rate of multiplication can 

 hardly occur since growth would be checked by scarcity of food or 

 by the accumulation of excreta from the bacteria themselves. The 

 rate of multiplication under most favorable conditions is the best 

 measure of the intensity of life processes, and in the case of pathogenic 

 bacteria, of virulence. The "generation period" is the time interval 

 between fissions in the same bacillus. This varies greatly with varying 

 conditions. Some of these conditions seem inherent in the strain while 

 others are more variable. Under most favorable conditions the 

 cholera bacillus has been found to divide about every half hour. When 

 a culture tube is inoculated there is a variable period during which 

 there is no multiplication, then fission begins. As the culture grows 

 older the rate of multiplication falls on account of the accumulation 

 of metabolic products. In infection the rate of multiplication is 

 determined by the number of bacteria introduced as well as by other 

 conditions. However, one strain of the same species may multiply 

 a thousand times as fast as another. 



Antagonism. As happens in all forms of life, the most destructive 

 agents to bacteria are other bacteria. It is fortunate that this is true, 

 and man and other animals profit greatly by the conflict continually 

 being waged between different species of bacteria. A drinking-water 

 supply becomes contaminated with the typhoid bacillus which flourishes 

 for a few days and is then completely destroyed by other bacteria. 

 So true is this that by the time the disease has developed among 



