2- ^ : GENERA*. ^MORPHOLOGY AND BIOLOGY 



>aili,. and ^may.-sjiojv^ branching either true or false. The 

 minute structure of the elements comprising these filaments is 

 analogous to that of the lower forms. Their size, however, is 

 often somewhat greater. The lower forms sometimes occur in 

 filaments, but here every member of the filament is independent, 

 while in the higher forms there seems to be a certain inter- 

 dependence among the individual elements. For instance, 

 growth may occur only at one end of a filament, the other 

 forming an attachment to some fixed object. (2) The higher 

 forms, moreover, present this further development, that in certain 

 cases some of the elements may be set apart for the reproduction 

 of new individuals. 



Terminology. The term bacterium of course in strictness 

 only refers to the rod-shaped varieties of the group, but as it 

 has given the name bacteriology to the science which deals with 

 the whole group, it is convenient to apply it to all the members 

 of the latter, and to reserve the term bacillus for the rod-shaped 

 varieties. Other general words, such as germ, microbe, micro- 

 organism, are used as synonymous with bacterium, though these 

 are often made to include the smallest organisms of the animal 

 kingdom. 



While no living organisms lower than the bacteria are known 

 (though certain facts regarding ultra-microscopic forms of life 

 make the occurrence of such possible), the upper limits of the 

 group are difficult to define, and it is further impossible in the 

 present state of our knowledge to give other than a provisional 

 classification of the forms which all recognise to be bacteria. 

 The division into lower and higher forms, however, is fairly well 

 marked, and we shall therefore refer to the former as the lower 

 bacteria, and to the latter as the higher bacteria. 



Morphological Relations. The relations of the bacteria to the animal 

 kingdom on the one hand and to the vegetable on the other constitute a 

 somewhat difficult question. It is best to think of there being a group 

 of small, unicellular organisms, which may represent the most primitive 

 forms of life before differentiation into animal and vegetable types had 

 occurred. This would include the flagellata and infusoria, the myxo- 

 mycetes, the lower algre. and the bacteria. To the lower algae the bacteria 

 show many similarities. These algae are unicellular masses of protoplasm, 

 having generally the same shapes as the bacteria, and largely multiply by 

 fission. Endogenous sporulation, however, does not occur, nor is motility 

 necessarily associated with the possession of flagella. Also their proto- 

 plasm differs from that of the bacteria in containing chlorophyll and 

 another blue-green pigment called phycocyan. From the morphological 

 resemblances, however, between these algse and the bacteria, and from 

 the fact that fission plays a predominant part in the multiplication of 

 both, they have been grouped together in one class as the Schizophyta 



