s typhosus, etc.). There are, however, a certain few
organisms which commonly express their pathogenicity in the formation of
pus. These are usually grouped together under the title of "pyogenic
bacteria," as distinct from those which only occasionally exercise a
pyogenic role.

The organisms included in this group are:

1. Staphylococcus pyogenes albus.
2. Staphylococcus pyogenes aureus.
3. Staphylococcus pyogenes citreus.
4. Streptococcus pyogenes longus.
5. Micrococcus tetragenus.
6. Bacillus pyocyaneus.
7. Bacillus pneumoniae.

and in certain special tissues

8. Micrococcus gonorrhoeae.
9. Micrococcus intracellularis meningitidis (Meningococcus).
10. Micrococcus catarrhalis.
11. Bacillus aegypticus (Koch-Weeks Bacillus).

The group may with advantage be subdivided as indicated in the following
pages:

I. _Pyogenic cocci._

Staphylococcus pyogenes albus.
Staphylococcus pyogenes aureus.
Staphylococcus pyogenes citreus.
to contrast with
Micrococcus candicans.
Micrococcus agilis.

1. Prepare subcultivations from each:

Bouillon, }
Agar streak, }
Blood serum, }
Litmus milk. } and incubate at 37 deg. C.
Agar streak, }
Gelatine stab, }
Potato. } and incubate at 20 deg. C.

Compare the naked-eye appearances of the cultures from day to day. Note
M. agilis refuses to grow at 37 deg. C.

2. Make hanging-drop preparations from the bouillon and agar
cultivations after twenty-four hours' incubation. Examine
microscopically and compare. Note the locomotive activity of M. agilis
and the Brownian movement of the remaining micrococci.

3. Prepare cover-slip films from the agar cultures, after twenty-four
hours' incubation. Stain for flagella by the modified Pitfield's method.
Note M. agilis is the only micrococcus showing flagella.

4. Make microscopical preparations of each from all the various media
after twenty-four and forty-eight hours and three days' incubation.
Stain carbolic methylene-blue, carbolic fuchsin, and Gram's method.
Examine the films microscopically and compare. Note in the Gram
preparation, the Gram negative character of certain individual cocci in
each film prepared from the three days' growth--such cocci are dead.

5. Stain section of kidney tissue provided (showing abscess formation
by Staphylococcus aureus) by Gram's method, and counterstain