In culture upon the ordinary media streptococcus is comparatively slow-growing, producing minute white colonies on or about the sixth day. It does not liquefy gelatine, and remains strictly localised to the track of the inoculating needle. Like the staphylococcus, it readily loses virulence. The thermal death-point is, however, lower: 54° C. for ten minutes. Marmorek has devised a method by which the virulence may be greatly increased, and he holds that it depends upon the degree of virulence possessed by any particular streptococcus as to what effects it will produce. By the adoption of Marmorek's methods attempts have been made to prepare an antitoxin.
Streptococcus pyogenes has been isolated from the membrane of diphtheria, and from small-pox, scarlet fever, vaccinia, and other diseases. In such cases it is not the causal agent, but merely associated with the complications of these diseases. Suppuration and erysipelas are the only pathological conditions in which the causal agency of streptococcus has been sufficiently established.
3. The Bacillus pyocyaneus occurs in green pus, and is the cause of that colouration. Gessard was the first to prove its significance, and he describes two varieties.
Micrococcus Tetragonus
It is a minute, actively motile, non-sporulating bacillus, which occasionally complicates suppuration and produces green pus. Oxygen is necessary for pigmentation, which is due to two substances: pyocyanin, a greenish-blue product extracted with chloroform, and pyoxanthose, a brown substance derived from the oxidation of the former pigment. Both these colours are produced in cultivation outside the body. On gelatine the colour is green, passing on to olive. There is liquefaction. On potato we generally obtain a brown growth (compare Bacillus coli, B. mallei, and others). The organism grows rapidly on all the ordinary media, which it has a tendency to colour throughout.
It will be remembered that when speaking of the antagonism of organisms, we referred to the inimical action of Bacillus pyocyaneus upon anthrax.
4. Micrococcus Tetragonus. This species occurs in phthisical cavities and in certain suppurations in the region of the face. It is a micrococcus usually in the form of small tetrads. A capsule is always present and sometimes discernible.
5. Bacillus coli communis and many putrefactive germs commonly occur in suppurative conditions, but they are not restricted to such disorders (see p. 64).
