18 MIGULA’S CLASSIFICATION OF BACTERIA 
Most of the known specific causes of the infectious diseases of 
animals are bacteria. It is necessary, therefore, in carrying out 
the above plan to choose from among the numerous classifications of 
bacteria one to be followed in grouping the diseases according to 
the genera of bacteria producing them. Of these the one by Migula 
seems to be the simplest and best adapted for this purpose and 
consequently it is selected. The only radical difference between 
this classification and the older ones, so far as pathogenic forms are 
concerned, rests in the fact that the old genus Bacterium is revived, 
but with a new meaning. All rod-shaped, non-motile bacteria 
are placed in this genus. This causes a change of the generic name 
from Bacillus to Bacterium of a number of pathogenic bacteria, 
such as those of tuberculosis, anthrax, swine plague and a few others. 
The same system should be followed with the diseases caused by 
fungi and protozoa. There are as yet so few species of fungi known 
to produce diseases in animals that their classification is not essential 
in discussing the few morbid conditions which they cause. The 
classification of protozoa by Calkins as found in his excellent work, 
“The Protozoa,” is observed for the grouping of the protozoan 
diseases. 
Migula’s classification of bacteria. The genera of the five families 
are included. 
FAMILIES 
I. Cells globose in a free state, not elongating in any direction before 
division into 1, 2, or 3 planes.............. 1. CoccacrZ. 
II. Cells cylindrical, longer or shorter, and dividing in only 1 plane, 
and elongating to twice the normal length before the division. 
(1) Cells straight, rod-shaped, without sheath, non-motile, or motile 
by means of flagella...... 12... .... 2. BacrERIAcEa. 
(2) Cells crooked without sheath.. ..... ... 3. SPIRILLACEZ. 
(3) Cellsenclosed in a sheath ...... 4. CHLAMYDOBACTERIACEAS. 
(4) Cells destitute of a sheath, united into threads, motile by means 
of an undulating membrane........ 5. BEGGIATOACEA. 
Coccacra®, cells without organs of motion. 
a. Division in 1 plane..... na? Naecurg css .. . Streptococcus. 
b. Division in 2 planes..... bees eeee cee. 2s. Micrococcus. 
c. Division in 3 planes..... 0... 0... 00.00 1c, Sarena. 
Cells with organs of motion. 
a, Division in 2 planes................. ..... Planococcus. 
b. Division in 3 planes.. ....  ............. Planosareina. 
BactEriace#, cells without organs of motion...... Bacterium. 
