128 BACTERIOLOGY. 



Some observers believe that the movement of 

 cocci is due to the existence of a flagellum. In 

 Bacterium termo the existence of a lash at either end 

 was first determined by the researches of Dallinger 

 and Drysdale. In motile bacilli, such as the hay 

 bacillus and Bacillus ulna, and in vibrios and spirilla, 

 the flagella can be readily recognised by expert 

 microscopists with the employment of the best 

 lenses, and, what is of equal importance, proper 

 illumination. They are objects of extreme delicacy, 

 and tenuity, and in stained preparations may be 

 absent from retraction or injury. Koch succeeded 

 in photographing them after staining with logwood, 

 which turned them a brown colour. They may also 

 be stained with the aniline dyes, for the author has 

 observed them in vibrios in preparations stained 

 with gentian violet, from which also they have been 

 photographed, in spite of the violet colour, by the 

 use of isochromatic dry plates. 



It is not certain whether the flagella are exten- 

 sions of the cell-wall, or derived from the internal 

 protoplasm. Van Tieghem holds the first view, and 

 does not regard them as motile organs at all. Zopf, 

 on the other hand, adheres to the second view, and 

 moreover believes that they can be retracted within 

 the cell-wall. 



Reproduction. Bacteria multiply by fission, 

 and by processes which may be considered as 

 representing fructification. The bacteria exhibiting 

 the latter processes have been divided into two 



