ORGANIZATION OF THE BACTERIA. 29 



swollen in the middle, with their extremities 

 rounded, such as certain forms of Vibrio serpens 

 (Warming) ; others again are fusiform, swollen in 

 the middle and attenuated at the extremities, 

 Bacterium fusiforme (Warming) ; rectilinear bac- 

 teria swollen at the two extremities are met 

 during the life of certain species, B. lineola and 

 B. termo, for example, above all when they are 

 transported to a more favorable medium : this 

 modification usually precedes segmentation ; final- 

 ly, one meets sometimes bacteria swollen at one 

 extremity only; the swollen part presents often 

 a clear point and sometimes an evident spore : we 

 shall see later the signification of this peculiarity. 

 With these claviform bacteria we may include the 

 Bacterium capitatum Dav., the Helobacteria of 

 Billroth, and certain Amylobacter, with heads of 

 the Ficus carica, etc. (Ch. Robin). 



The undulating bacteria constitute the Vibrios 

 properly so called (V. rugula, serpens, etc.). 



The spiral bacteria of which the turns are more 

 or less elongated are named Spirillum, Spiro- 

 chceta, etc. 



Dimensions. The dimensions of the bacteria 

 oscillate between the most variable limits, but in 

 a general way it may be said that they are the 

 smallest of all microscopic beings. Some of them 

 are situated at the extreme limit of our highest 

 magnifying powers ; and their proportions, as to 



