GENERAL CHARACTERS OF BACTERIA. 
threads of bacteria, and which may show frequent branching, a 
characteristic not usual in bacteria. They also have a peculiar 
method of forming reproducing bodies. The group is not one of 
very great importance. One type of Streptothrix is extremely 
abundant in soil and appears as round, white opaque colonies with 
an extensive brown halo upon the plates described in Experiment 
No. 24. 
Thus it will be seen that the term bacteria applies to the whole 
group of organisms that multiply by division, the study of which 
constitutes the study of bacteriology, while 
the term Bacterium refers to a single division 
of the group, viz.: the non-motile, rod forms. 
The term Bacillus should apply to motile 
forms only. The names Bacillus and Bac- 
terium are sometimes confused; for example, 
the tubercle bacillus, according to the above 
classification, is a Bacterium, since it is non- 
motile; and indeed re*cent study indicates that 
it belongs to the group of higher fungi; but the 
name bacillus was given it years before the 
above distinctions were recognized, and we 
will still use the common name. Some other 
bacteria, named twenty years ago, retain their 
earlier names in some books, but they are 
slowly having their names brought into 
harmony with the above distinctions. 
The term Coccus is applied to any spherical organism of the 
group bacteria. 
This classification gives only what are recognized as the genera 
of bacteria. A further classification of the group into species is at 
the present time in a condition of the greatest confusion. Many 
hundred varieties have been described by different bacteriologists, 
but there is great difficulty in giving any distinctive description of 
such minute organisms, which have so few characters; and it is 
quite uncertain whether these many hundred described species 
represent distinct forms or whether they should be reduced to a 
FIG. 10. Actinomy- 
ces. a. a small colony; 
b, single rods (Bostrom). 
