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and it is in such fluid media that the chain-formation is best developed. In preparing the cover-glass from this as little manipulation of the fluid as possible should be used, in order to avoid destroying the chain arrangement.

Practically, the only organism with which the streptococcus may be confounded is the pneumococcus, which also grows in minute colonies and sometimes in chains. The streptococcus may be distinguished from the pneumococcus, however, by the morphology of the individual organisms, the streptococci appearing as pairs of hemispheres, and the pneumococci as pairs of oval, conical, or lancet-shaped organisms, the broader ends of which are in apposition. Stains by Gram's method.

Bouillon. The character of the growth in bouillon is subject to considerable variation, and certain doubtful varieties of the streptococcus are distinguished mainly by the bouillon culture.

"We thus distinguish short-chained streptococci ('streptococcus brevis '), long-chained streptococci (streptococcus longus), streptococci which render bouillon cloudy and those which do not, streptococci which form flocculent or scaly or sandy or viscous sediments.

"The name streptococcus conglomeratus' is given to a streptococcus which grows, without clouding the bouillon, in the form of dense, separate particles, scales, or thin membranes at the bottom or sides of the tube, and on shaking the sediment it breaks up into little specks, without producing uniform diffuse cloudiness.

"On microscopical examination the chains in the latter case are long and interwoven in conglomerate masses. Streptococcus chains may be straight or wavy or twisted. These various distinctions are only of relative value. One form may change into another. Virulent streptococci may be found among all the groups mentioned; the streptococci of erysipelas and most of the streptococci from abscesses and septicemia grow in long chains in bouillon" (Welch). Agar-agar Slant.-Minute grayish translucent colonies (Fig. 30).

Agar-agar Stab.-Small spherical grayish colonies along the needle-track.

Gelatin.-Growth similar to that on agar-agar.

Litmus-milk.-Some varieties turn the medium pink and cause coagulation.

Pathogenesis.-The results of the inoculation of animals are not constant, great variation in the virulence of different cultures being observed. Sometimes mice inoculated at the root of the tail or in the peritoneal cavity will die in about twenty-four hours with enlargement of the spleen and large numbers of the organism in the internal organs.

Occurrence.-The streptococcus occurs frequently in the spreading phlegmonous inflammations as well as in suppurative processes generally, and is the most common cause of septicemia. It is almost always present in inflammatory conditions of the mucous membrane of the pharynx, and is often encountered in broncho-pneumonia. In erysipelas it is almost invariably the infecting organism, and it is the most frequent cause of puerperal septicemia. In the majority of fatal cases of diphtheria and in some cases of typhoid fever, scarlet fever, tuberculosis, and other acute inflammatory diseases it will be found in the blood of the various internal organs after death. It also occurs in a certain proportion of cases of peritonitis, pleuritis, meningitis, endocarditis, and otitis media. Gaining entrance to the tissues through an insignificant wound or abrasion of the skin, it may produce a rapidly fatal septicemia in a susceptible individual, in whose internal organs at autopsy large

[graphic]

FIG. 30.-Streptococcus

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

numbers of the organism will be found. This general invasion of the circulation may also be observed in cases of chronic or wasting disease, the infection occurring during the last days or hours of life (terminal infection).

Of other conditions in which it may occur, hepatic abscess, appendicitis, osteomyelitis, and synovitis may be mentioned. Although the streptococcus is distinctly one of the pus-producing bacteria, yet the inflammations of the soft parts of the extremities which are produced by it are generally characterized more by necrosis and serous or hemorrhagic exudation and infiltration than by the breaking down of tissue and frank pus-production. In this the organism is in marked contrast to the staphylococcus pyogenes aureus, which practically always produces dissolution of tissue and pus. Moreover, the streptococcus inflammations are more commonly accompanied by lymphangitis than are those due to the staphylococcus pyogenes aureus.

In a few instances we have met with a streptococcus whose colonies assume a well-marked yellow color on blood-serum, but which in other respects are like the long-chained forms above described.

Diagnosis.-The streptococcus pyogenes may often be identified by the cover-glass examination alone through its characteristic chain-formation, but this may not be apparent and the result of cultures must then be awaited.

Erysipelas.-The streptococcus is most readily found in the extreme margin of the affected area where the process is newest. The skin should be cleansed with soap and water, and with alcohol. Then with a sterile knife-point or a large needle a small wound should be made, and some of the blood and exudate pressed out from the tissue beneath. From this, cultures and cover-glasses may be prepared.

Pneumococcus.'-Synonyms: Diplococcus pneumoniæ ; Micrococcus lanceolatus; Micrococcus of sputum-septicemia; Micrococcus pneumoniæ crouposæ.

1A. Fränkel: Zeitschrift für klinische Medicin, Bd. x. u. xi.; Weichselbaum: Wiener med. Jahrbücher, 1886.

Blood-serum.-Minute colorless, transparent colonies, resembling very small drops of dew (Fig. 34).

Morphology-Pairs of rather small oval, conical, or lancetshaped organisms, the broader ends being in apposition.

[graphic]

FIG. 31.-Pneumococci from a culture; X 2000 (Wright and Brown).

The organism varies somewhat in size, and one of the "pair" may be smaller than the other (Fig. 31). In some cases atypical or involution forms are seen, especially if the culture.

[graphic]

FIG. 32.-Pneumococci with capsules in a cover-glass preparation from sputum stained by Gram's method and Bismarck brown; X 2000 (Wright and Brown).

be more than twenty-four hours old. No capsules are ordinarily observed in cultures with ordinary methods of staining. In the "water of condensation" of the blood-serum tube, chains may be formed resembling those of the streptococcus,

but differing from the chains of that organism by the oval or lancet form of the elements of which they are composed.

In pus, blood, or in other material, the organism is invested with a hyaline zone, called the capsule (see Figs. 32, 33). This is composed of a mucin-like substance. It may be seen usually in cover-glass preparations stained by the ordinary methods, especially if the preparations be examined in water-mounting:

[graphic]

FIG. 33-Diplococcus pneumoniæ; cover-glass preparation from the heart's blood of a rabbit; X 1000 (Fränkel and Pfeiffer).

Stained by Gram's method. Not motile.

Glycerin Agar-agar.-Feeble growth of very minute grayish colonies.

Bouillon-Clouded faintly.

Litmus-milk.-Sometimes turned pink and coagulated. Growth on other culture-media is very feeble. The organism dies out rapidly in cultures. To keep it viable it should be transplanted every forty-eight hours.

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