16 



BACTERIOLOGY. 



movements on the surface of solid nutrient gelatine. Groups of 

 rods may be observed to pass each other in opposite directions. 

 Single individuals meet and progress side by side, or one or more 

 individuals may part from a group and glide away independently. 

 Occasionally a number of rods progress in single file. It is, however, 

 difficult to believe that these movements can occur on a solid surface. 



Fig. 3. — Flagella. 



1. Coccus with flagellum. 2. Similar coccus dividing, with two flagella. 3. Colony 

 of flagellated macrococci of Beggiatoa roseo-persicina. 4. Short rod from the 

 same Beggiatoa with flagella [all after Zopfj. 6. Bacillus with flagella [from 

 a photograph by Koch]. 6. Bacillus subtilis [after Brefeld]. 7, 8. Short rod- 

 forms of Beggiatoa roseo-persicina with one flagellum [after Zopf]. 9. Very 

 long rod of the same, with flagellum at both ends [after Warming]. 10. Vibrio, 

 with double flagellum at each end [after Warming]. 11. Vibrio, with flagella 

 [from a photograph by the author]. 12. Spirillum with flagella [from a photo- 

 graph by Koch]. 13. Spirillum with flagella [after Zopf]. 14. Spirillum with 

 double flagella [after Zopf]. 15. Beggiatoa roseo-persicina, with a triple 

 flagellum at one end ; and 16, with a double flagellum at both ends [after 

 Warming]. 



The author is inclined to beheve that there is an almost inappreciable 

 layer of liquid on the surface of the gelatine, which is expressed 

 after the gelatine sets. In tubes of nutrient agar-agar gelatinised 

 obliquely and then kept upright the liquid so expressed collects at 

 the bottom of the sloping surface. 



