Microbial Structures and Staining Reactions 103 



THERMOPHILIC ( heat-loving ) bacteria are much more resistant to 

 heat, whereas vegetative bacteria are killed by an exposure to a 

 temperature of 65-80° C. moist heat for only a few minutes. 



Fortunately, few spore-formers are capable of causing disease in 

 man. But the most important ones are probably Clostridium 

 tetani, the cause of lockjaw, Clostridium perfringens, the etiological 

 agent of gas gangrene, the previously mentioned Clostridium 

 hotulinum, and Bacillus anthracis, the biological agent in anthrax. 



FLAGELLA 



Rapid locomotion by bacteria is not uncommon, and this move- 

 ment is brought about principally through the influence of hair- 

 like projections termed flagella ("little whips"). All spirals are 

 motile, probably half of the rods are motile, and practically none 

 of the cocci exhibit independent movement. The position and 

 the number of flagella will vary between species, but constancy 

 of arrangement of flagella is an aid in the identification of species. 



Since bacteria are single-celled organisms, we must consider the 

 flagella to be a continuation of the cell with a direct connection 

 to the underlying cytoplasm. The electron microscope substantiates 

 this claim. Electronographs reveal many flagella to be much 

 longer than the cells from which thev arise, so it is not too sur- 

 prising to find free flagella floating around in a medium, since 

 flagella are delicate and can be broken off by even gentle agitation. 



Motility is a valuable asset to bacteria, just as it is important 

 to man and to other animals. The chances of survival are greatly 

 enhanced when an organism has an opportunity to go out and look 

 for food if the supply begins to run low. Being trapped in an 

 unfavorable locality without means of escape can be as critical for 

 a bacterium as it is for a helpless bedridden patient in a locked 

 room that has caught fire when no one is around to offer assistance. 



One of the topics of the day in active bacteriological circles is 

 this entire question of flagella. Do bacteria have them, or are they 

 artifacts which appear as a result of locomotion? Are flagella the 

 cause or the effect of motility? Until definitely proven othersvise, 



