REPRODUCTION BY MEANS OF SPORES 7^3 



entering into a state of rest for a time, after which they may 

 resume active growth: such resting-cells are frequently termed 

 arthrospores. cs C3 , , 



4. Although there is little doubt ' ^ ^ 



that a large number of distinct species ^7 yp ,-<?^^ 



of bacteria exist, the classification of . *-f «a 



these organisms into species and / 



ffenera is rendpreH HiffiniU nn nr Fig- =6^.-1, 2 and 3. Diagrammatic 

 gciicrd, lb renuereu Uimcuu on ac representation of the successive stages 



rniint nf tVlpir miniltp Himpnoinna of germination of a bacterium spore. 

 count 01 meir minute Qimensions ^_5_ 5 and 7. Another common method 



and the simplicity of their organisa- ofg^mmationofa bacterium spore. 

 tion; besides, their form, which has been taken as a basis of 

 classification, is subject to variation, for example a species oc- 

 curring usually in the form of a bacillus may under some con- 

 ditions appear as a coccus. Moreover, the attempts to define 

 the limits of each species by taking into consideration its power 

 of producing spores, the presence or absence of cilia and other 

 variable characters of the organism have not yet led to any com- 

 plete or satisfactory system of classification. The names which 

 at present are most commonly in use for what are supposed to 

 be distinct species are double as in the case of higher plants ; 

 the first or generic name indicates the form which the bacterium 

 most frequently assumes, while the second or specific name often 

 denotes some physiological or other peculiarity : for example, 

 the organism which is met with in the form of a bacillus, and 

 is the cause of the disease tetanus or lockjaw, is named Bacillus 

 teiani : another occurring in the form of a coccus and capable 

 of producing lactic acid from sugar is known as Micrococcus 

 acidi lactici. 



5. On account of their small size and consequent lightness, 

 bacteria are readily blown about by the wind and carried in 

 streams of water to all parts of the earth. Wherever decay and 

 putrefaction of organic substances are going on, they are present 

 in especial abundance and are met with in enormous numbers 

 in the air, in the upper regions of the soil, on our clothes and 



