126 BACTERIOLOGY. 



straight thread-forms, which are motile, the move- 

 ment is very slow and vermicular in character, but 

 in wavy threads, such as the Spirochcete plicatilis, 

 there is not only an undulatory motion, with rapid 

 progression across the field of the microscope, but 

 if they are confined by more or less ddbris, they 

 give very peculiar and characteristic spasmodic 

 movements. 



The rod-forms of Proteus vulgaris exhibit very 

 extraordinary 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. The author is inclined to 

 believe 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. 



What the means are by which bacteria are en- 

 dowed with the power of spontaneous movement 

 and of progression may still be said to be unsettled. 

 The author has watched the movement of long 

 slender threads in sewage-contaminated water, 

 which could only be explained by the inherent 



