METHODS OF REPRODUCTION 9 



species differ in dimensions, but considerable differences 

 may be noted in a pure culture of the same species. On 

 the other hand, there are numerous species which so closely 

 resemble each other in size and shape that they cannot be 

 differentiated by microscopic examination alone, and we 

 have to depend upon other characters, such as colour, 

 growth in various culture media, pathogenic power, 

 chemical products, etc., to decide the question of identity. 



Methods of Reproduction. — The reproduction of bacteria 

 takes place by ' fission ' or by ' spore ' formation. Fission 

 is a process of splitting, or division, whereby an organism 

 divides into two parts, each of which lives on and divides in 

 its turn. If an organism is watched under the microscope, 

 the coccus or bacillus, as the case may be, will be seen to 

 elongate somewhat, and at the same time becomes narrower 

 and narrower, until its two halves become free, the two in- 

 dividual organisms so produced again dividing in their 

 turn. ,If, however, the new organisms do not break away 

 from each other, but remain connected in groups or clusters, 

 they are known as staphylococci ; if they remain connected 

 in the form of chains, like a string of beads, they are known 

 as streptococci. If the division in the case of cocci takes 

 place in one plane, diplococci are formed. If division takes 

 place in two directions, tetracocci or tablet-cocci are 

 formed. Again, if the division is in three directions, sarcina 

 or packet-cocci are formed. On account of this multiplica- 

 tion by fission, the generic name of schizomycetes, or 

 ' fission-fungi,' has been given to the bacteria. Some 

 species, such as the various Cladothrices, do not divide, 

 but grow in length, and give rise to branched threads. 



The second method by which the bacteria propagate is 

 by the development of spores. These are distinguished by 

 their remarkable power of resistance to the influence of 

 temperature and the action of chemical agents and other 



