MORPHOLOGY AND PHYSIOLOGY OF BACTERIA. 



17 



The means by which bacteria are endowed with the power of 

 spontaneous movement and of progression may still be said, in 

 some cases, to be unsettled. The author has watched the move- 

 ment of long slender threads in sewage-contaminated water, which 

 could only be explained by the inherent contractiUty of the proto- 

 plasmic contents ; for if any drawing or propelUng organ existed 

 in proportion to the length of the organism, it would probably have 

 been visible. But in many cases the organism is provided with a 

 vibratile lash or flagellum stt one end, or with one or more at both 

 ends, or with numerous lateral and terminal flagella. 



Some observers believe that the movement of cooci is due to the 



Tig. 4. — Bacillus megatherium. 



a. A chain of rods, x 250. The rest x 600. 



b. Two active rods. 



d to /. Successive stages of spore-formation. 

 h to m. Successive stages of germination. 



[After De Bary.] ' 



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 prepara- 

 tions may be absent from retraction or injury. Koch succeeded 

 in photographiag them after staining with logwood, which turned 

 them a brown colour. 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 



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