STRUCTURE AND CONSTITUENTS OF BACTERIAL CELL 29 



flagellum at one or both ends of the organism; in the typhoid bacillus 

 they are distributed around the sides of the organism but do not occur 

 at the ends. 



Spores. Endospores. Many bacteria die when their environment 

 becomes unsuited for further growth. Death may result from the 

 presence of inimical substances, the absence of essential foods, or the 

 intervention of unsuitable physical conditions. Death is manifested 

 by a cessation of chemical interchange between the bacterial cell and 

 its environment. There is a group of bacteria, however, usually of 

 saprophytic origin, which is able to survive even prolonged exposure 

 to unfavorable environmental conditions by passing into a latent stage 

 during which chemical interchange with the environment is at an 

 extremely low ebb. This latent stage or hibernation has been known 

 to last for more than two decades in certain instances, and yet the 

 organisms have resumed their original luxuriant growth when placed 



<*> 



FIG. 3. Types of bacterial spores. 



under favorable conditions. The bacteria which exhibit this latent 

 state produce within their substance highly refractile, spherical or oval 

 bodies called spores. Spores are not found in very young, actively 

 growing cultures, as a rule. Spore formation is ushered in by a clouding 

 of the endoplasm of the bacterial cell, which gradually becomes granular. 

 The granules coalesce, eventually appearing as the mature spore which 

 is surrounded by a dense membrane, frequently exhibiting a double 

 contour when stained by dilute carbol fuchsin. 1 The spore membrane 

 (ectoplasm) is relatively impermeable to heat and disinfectants and 

 confers the resistance to physical agents which spores exhibit upon 

 them. But one spore is formed in an individual bacterium, except 

 under most unusual conditions. It is to be emphasized, consequently, 

 that spore formation is not a reproductive process. The mature spore 

 may form in the center of the bacterium, at, or near one end. The 

 spore may be round or oval, and greater or lesser in diameter than 

 the parent cell. If the spore is greater in diameter it distends the 

 cell membrane, producing a spindle-shaped organism if the spore is 



1 Meyer, A., Practicum der botanischen Bakterienkunde, Jena, 1903. 



