10 



BACTERIOLOGY FOR NURSES 



to and fro movement which serves to propel the bacterium through 

 the liquid in which it is growing (Fig. 3). 



FIG. 3. Arrangement of Flagella. 



The arrangement of the flagella varies in the different species of 

 bacteria. Following is a classification according to their number 

 and distribution : 



The degree of motility depends upon the species, the age of 

 growth, heat, light, the presence of chemicals, etc. The property 

 by means of which bacteria are aware of the various forces which 

 influence them is known as taxis. When they are attracted the 

 phenomenon is spoken of as positive taxis, when they are repelled 

 as negative taxis. 



Spore Formation. Under certain circumstances some species 

 of bacteria produce changes in their protoplasm which result 

 in the formation of bodies known as endospores, and to these 

 new bodies all the vital powers of the original cell are transferred. 

 Its commencement in a bacterium is indicated by the endoplasm 

 becoming turbid and the appearance of minute refractile granules 

 which do not readily take the ordinary stains. By degrees the 

 granules become larger and finally coalesce into a spherical or 

 oval body, always shorter but often broader than the original 

 bacterium. Surrounding the endospore is a dense protective 

 envelope which is supposed to give to the spore its characteristic 



