42 PA THOGENIC BACTERIA.

It has even been suggested to classify the bacteria by
the size and number of their fiagella, of which so little
is known.

The most convenient classification, though it cannot
be purely scientific, seems to be the morphological one *
given by Cohn. Baumgarten, recognizing the relative
pleomorphism of certain of the species, has modified it
as follows, and thus made it answer all the needs of the
pathologist at least:

I. Cocci, \

II. Bacilli, I species relatively monomorphous.

III. Spirilla, J

IV. Spirulina, \

V. Leptothrix, > species relatively pleoinorplious.
VI. Cladothrix, J

The members of the first group, the cocci, bacilli, and
spirilla, are practically the only ones which are of patho-
logical significance.