vin NATURE OF GENERIC FORMS 89 



remaining in contact, form a long wavy or twisted filament 

 called Leptothrix (Fig. 16) the separate elements of which 

 are usually only visible after staining. 



Bacillus also multiplies by a peculiar process of spore- 

 formation which may take place either in the ordinary resting 

 form or in a Leptothrix filament. A bright dot appears at 

 one place in the protoplasm (Fig. 1 8) : this increases in size, 

 the greater part of the protoplasm being used up in its 

 formation, and finally takes on the form of a clear oval 

 spore which remains for some time enclosed in the cell-wall 

 of the Bacillus, by the rupture of which it is finally liberated. 

 In other Bacteria spores are formed directly from the ordin- 

 ary cells which become thick walled. The spores differ 

 from the Bacilli in being unstained by aniline dyes. 



After a period of rest the spores, under favourable cir- 

 cumstances, germinate by growing out at one end so as to 

 become rod-like, and thus finally assuming the form of 

 ordinary Bacilli. 



There are other genera often included among Bacteria, for 

 the description of which the student is referred to the more 

 special treatises.^ One remark must, however, be made in 

 concluding the present brief account of the morphology of 

 the group. There is a great deal of evidence to show that 

 what have been spoken of as genera (Bacterium, Bacillus, 

 Spirillum, &c.) may merge into one another and are there- 

 fore to be looked upon as phases in the life-history of 

 various microbes rather than as true and distinct genera. 

 But this is a point which cannot at present be considered 

 as settled. 



The conditions of life of Bacteria are very various. Some 



live in water, such as that of stagnant ponds, and of these 



^ See especially De Bary, Fungi, Mycetozoa, and Bacteria (Oxford, 

 1887), and Klein, Micro-organisms and Disease (London, 1896). 



