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 ot 
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- 
cheeta, ete. | 
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 
