MORPHOLOGY OF BACTERIA 23 



proposed a classification of bacteria based upon the num- 

 ber and arrangement of the flagella. 



Spores. Spores are small spherical or oval highly re- 

 fractive bodies which develop in the body substance of cer- 

 tain species of bacteria. There is no difference in the proto- 

 plasm of the spores, however, from that of the contents of 

 the organisms. They contain all of the proteins of the par- 

 ent cell and when developed are surrounded by a thin sub- 

 stance inside the otherwise empty shell or cell wall of the 

 organism. This cell wall softens or dissolves and the spore- 

 is then set free. Free spores are frequently observed in 24r 

 hour cultures when the growth occurs under favorable con- 

 ditions. Usually, however, they are not set free until they 

 are much older. They are characterized by their power to- 

 resist injurious influences, such as heat, dessication and dis- 

 infectants. The spores of different species of bacteria dif- 

 fer in the degree of their resisting power. Bacteria produce 

 endospores. Arthrospores do not appear to exist among 

 any of the bacteria. To observe the form of the spores of 

 any species it is well to employ a streak culture on agar or 

 potato, which should be kept at the temperature best suited 

 to the growth of the organism. After 12 hours and at short 

 intervals thereafter specimens of the culture should be exam- 

 ined in a hanging drop preparation, and if round or oval 

 strongly refractive bodies are observed within the bacteria, 

 they should be stained for spores. Individual bacteria rarely 

 contain more than one spore each; more than two have not 

 been observed. The formation of spores has been deter- 

 mined in a few spirals, in many rod-shaped bacteria, but not 

 in micrococci. The vast majority of bacteria do not pro- 

 duce spores. The conditions of. spore formation are not 

 fully understood. 



According to Fischer, motile bacteria always come to 

 a state of rest or immobility previous to spore formation. 

 Several species first become elongated. The anthrax bac- 

 terium does this, and a description of the method of its pro- 

 duction of spores may serve as an illustration of the process. 



