faction in the form of a long, narrow, blunt-pointed, inverted cone (Fig. 46) full of clouded liquid, at the apex

FIG. 46.-Staphylococcus pyogenes aureus: puncture-culture three days old in gelatin (Fränkel and Pfeiffer).

of which a collection of golden or orange-yellow precipitate is always present. It is this precipitate in particular that gives the organism its name, "golden staphylococcus."

The most characteristic growth is upon agar-agar. Along the whole line of inoculation an orange-yellow, moist, shining growth occurs. When the growth takes place rapidly, as in the incubator, it exceeds the rapidity of color-production, so that the centre of the growth is distinctly golden; the edges may be white.

Upon potato the growth is luxuriant, producing an orange-yellow coating over a large part of the surface. The potato-cultures give off a sour odor.

When grown in bouillon the organism causes a diffuse cloudiness.

In milk coagulation takes place, and is followed by gradual digestion of the casein.

The Staphylococcus albus is exactly the same as the aureus, with the exception that in all media it is constantly colorless.

Experiments have shown that the Staphylococcus aureus, like its congener, the albus, exists in an attenuated form, and there is every reason to believe that in the majority of instances it inhabits the surface of the body in this form.

When virulent the golden staphylococcus is a dangerous and often deadly organism. Its pathogeny among animals is decided. When introduced subcutaneously, abscesses almost invariably follow, except in a certain few comparatively immune species, and not infrequently lead to a fatal termination. In such cases the organisms may be cultivated from the blood of the large vessels, though by far the greater number collect in, and frequently obstruct, the capillaries. In the lungs and spleen, and still more frequently in the kidneys, infarcts are formed by the bacterial emboli. The Malpighian tufts of the kidneys sometimes are full of cocci, and become the centres of small abscesses.

The coccus is almost equally pathogenic for man, though the fatal outcome is much more rare. It enters the system through scratches, punctures, or abrasions, and when virulent generally causes an abscess, as various experimenters who inoculated themselves have discovered to their cost. Garré applied the organism in pure culture to the uninjured skin of his arm, and in four days developed a large carbuncle with a surrounding zone of furuncles. Bockhart suspended a small portion of an agar-agar culture in salt-solution, and scratched it gently into the deeper layers of the skin with his fingernail; a furuncle developed. Bumm injected the coccus. suspended in salt-solution beneath his skin and that of several other persons, and produced an abscess in every

case.

The Staphylococcus aureus is not only found in the great majority of furuncles, carbuncles, abscesses, and other inflammatory diseases of the surface of the body, but also plays an important rôle in a number of deeplyseated diseases of the internal organs. Becker and others obtained it from the pus of osteomyelitis, demonstrating that if, after fracturing or crushing a bone, the staphylococcus was injected into the circulation, osteomyelitis would result. Numerous bacteriologists have demonstrated its presence in ulcerative endocarditis. Rodet has been able to produce osteomyelitis without previous injury to the bones; Rosenbach was able to produce ulcerative endocarditis by injecting some of the staphylococci into the circulation in animals whose cardiac valves had been injured by a sound passed into the carotid artery; and Ribbert has shown that the injection of cultures of the organism may cause the valvular lesion without the preceding injury.

The Staphylococcus aureus is an easy organism to ob

FIG. 47. Streptococcus pyogenes, from the pus taken from an abscess; × 1000 (Fränkel and Pfeiffer).

tain, and can be secured by plating out a drop of pus in gelatin or in agar-agar. Such a preparation, however,

generally does not contain the Staphylococcus aureus alone, but shows colonies of the Staphylococcus albus as well. In addition to these two principal forms, one sometimes discovers an organism identical with the preceding, except that its growth on agar-agar and potato is of a brilliant lemon-yellow color, and its pathogeny for animals much less. This is the Staphylococcus citreus of Passet. It is not quite so common, and not so pathogenic as the others, and consequently much less important.

Another organism whose colonies are frequently obtained from the pus containing the staphylococci is the Streptococcus pyogenes of Rosenbach (Fig. 47). It was found by him in 18 of 33 cases studied, fifteen times alone and five times with the Staphylococcus aureus. It is a spherical organism of variable size (0.4-1 μ in diameter), constantly associated in pairs and chains of from four to twenty individuals.

The organism stains well with ordinary aqueous solutions of the anilin dyes, and also by Gram's method. Like the coccus already described, it is not motile and does not seem to form spores, though sometimes a large individual-much larger than the others in its chain-may be observed, and may suggest the thought of arthrosporulation.

Upon gelatin plates very small colonies of translucent appearance are observed. When superficial, they spread out to form flat disks about 0.5 mm. in diameter. The microscope shows them to be irregular and granular, to have a slightly yellowish color, and to have numerous irregularities around the edges, due to projecting chains of the cocci. No liquefaction occurs.

cus pyogenes: culture upon agar-agar two days old (Fränkel and Pfeiffer).

In gelatin puncture-cultures no liquefaction is observed. The minute spherical colonies grow along the whole needle-track and form a slightly opaque granular line.

Upon agar-agar an exceedingly delicate transparent growth develops slowly along the line of inoculation. It consists of almost transparent, colorless small colonies which do not become confluent.

The growth upon blood-serum much resembles that upon agar-agar. The streptococcus does not grow upon

potato.

The organism seems to grow well in milk which is coagulated and digested.

The Streptococcus is not very sensitive to acids, and can be grown quite well in media with a slightly acid reaction.

Sternberg found that the streptococci succumb to a temperature of 52-54° C. continued for ten minutes.

The streptococcus pyogenes is not very pathogenic for animals. Subcutaneous injections into mice and rabbits are, as a rule, without either general or local manifestations of importance. If, however, an ear of a rabbit is inoculated with a small amount of a pure culture carefully scratched in, a small patch resembling erysipelas usually results. The disturbance passes away in a few days and the animal recovers.

Like the staphylococci, the Streptococcus pyogenes is frequently associated with internal diseases, and has been found in ulcerative endocarditis and in the uterus in cases of infective puerperal endometritis. Its relation to diphtheria is of interest, for, while, in all probability, the great majority of cases of pseudo-membranous angina are caused by the Klebs-Löffler bacillus, yet an undoubted number of cases are met with in which, as in Prudden's 24 cases, no diphtheria bacilli can be found, but which seem to be caused by a streptococcus exactly resembling that under consideration.

There is no clinical difference in the picture of the throat-lesion produced by the two organisms, and the