28 PHARMACEUTICAL BACTERIOLOGY. 



from it in its higher refractive index and its peculiar resistance to the action of 

 stains. As soon as spore formation is complete, the rest of the cytoplasm 

 dies, the cell-wall disintegrates, and the spore is thus set free. Spores have 

 a remarkable resisting power to high temperatures and other unfavorable 

 conditions. In a dry atmosphere they may lie dormant for a long time, 

 even several years. Boiling from one to two hours does not kill some of 

 them (spores of hay bacillus). As soon as the spores are placed in suitable 

 media (adequate warmth, moisture, and food supply) they develop into new 

 individuals, which continue to septate until spore formation again takes 

 place. 



c=,c=, ^ x; CA 



Fig. g. — Illustrating polymorphism or pleomorphism. a to d, inclusive, represent 

 different forms of the same organism — the Diphtheria bacillus. (See also Figs. 46-50 

 inclusive.) 



Arthrospore formation is less common, and occurs mostly among the 

 micrococci. The entire cell is converted into a spore, which becomes some- 

 what enlarged and encapsuled, in which state it is enabled to tide over cer- 

 tain conditions unfavorable to normal growth and septation. Arthrospore 

 formation is not well understood as yet. It may also be that some of the 

 phenomena described as arthrospore formations are in reality endospore 

 formations. 



The classification given above, into families and genera, and Figs. 2 to 10, 

 inclusive, will serve to give a fairly good idea of the general structural char- 

 acteristics of microbes. 



3. General Physiology of Microbes. 



Microbes, in common with living things generally, spring from pre- 

 existing parents, take in and assimilate food, grow and multiply, and finally 

 die. The rate of growth and of multiplication (septation or division) varies 



