22 Bacteria in Relation to Country Life 



Other unfavorable conditions, such as partial ex- 

 ha,ustion of the food-supply, too great concentration 

 of the culture solution, and abnormal temperatures, 

 may contribute to check excessive multiplication. 



Spores. — ;As a defense against adverse conditions, 

 the bacteria have the power to produce cells known as 

 spores (Fig. 8). These are much more resistant to 

 destructive agents than are the ordinary cells. In form- 

 ing spores, bacteria, at first homogeneous, gradually 

 become granular. The granules thus formed coalesce 

 into a single glistening mass, which surrounds itself 

 with a cell-wall that is tough and not readily penetrated. 

 The newly formed spore may remain in the empty cell- 

 wall of the parent organism, or may pass out into the 

 surrounding medium. The number of such spores in- 

 creases with the age of the culture. 



Spores a means of preservation. — Spores may 1)6 

 called "bacterial eggs." They are, however, a means' 

 of . preservation rather than a means of multiplication. 

 The entire organism is transformed into a single spore. 

 Exceptions have been noted, in the case of one or two 

 species, in which a single organism produces two spores — 

 a fact that does not detract, however, from the truth 

 of the general statement. 



Spore formation. — Different species show variations 

 in the method of spore formation. With some of them, 

 the cells are transformed into boat-shaped or spindle- 

 shaped masses, containing the spore at one end or in 

 the middle. With others, the' cyUndrical shape of the 

 parent cell is retained on the spore located in the middle 

 or at one end. With still others, there may be a thicken- 



