The margin of the colony is sharply circumscribed; the interior is broken up. The gelatin is not liquefied. In gelatin punctures there is no liquefaction observable.

Upon agar-agar the development at the temperature of the incubator, which is more rapid than that at the temperature of the room, results in the production of a bluish-gray layer.

The growth upon potato has a brownish color. The growth in bouillon and in peptone solutions is accompanied by the production of indol.

The spirillum is pathogenic for mice, guinea-pigs, and canary birds.

Spirillum Weibeli.-This spirillum (Fig. 92) was found in 1892 by Weibel in spring-water which had a long time

FIG. 92. Spirillum Weibeli, from agar-agar; x 1000 (Itzerott and Niemann). before been infected by cholera. It is short, rather thick, and distinctly bent, often forming S-shaped figures.

The colonies before liquefaction sets in are described as pale-brown, transparent, circular, and homogeneous. Liquefaction is much more rapid than in cholera, and causes the borders of the colonies to become irregular. In the centre of each colony a little depression is observed.

In gelatin puncture-cultures the growth is rapid, be

ginning first upon the surface, where a large flat, saucershaped liquefaction, extending to the sides of the tube, forms. Scarcely any growth takes place in the puncture, but the superficial liquefaction, separated by a horizontal line from the normal gelatin, descends slowly.

Upon agar-agar a grayish-white layer is formed.
No growth has been obtained upon potato.

In alkaline peptone solution a slow but luxuriant growth takes place.

Spirillum Milleri.-This spirillum (Fig. 93) was found in the mouth by Miller in 1885. It resembles the cholera

FIG. 93.-Spirillum Milleri, from an agar-agar culture; x 1000 (Itzerott and Niemann).

spirillum somewhat, but is much more like the spirillum of Finkler and Prior, with which many bacteriologists think it identical.

Upon gelatin the colonies are small, finely granular, have a narrow border-zone and a pale-brown color. The gelatin is rapidly liquefied.

Upon agar-agar a thick yellowish layer is produced. The organism seems not to be pathogenic.

Spirillum Aquatilis.-Günther in 1892 found this organism (Fig. 94) in the water of the river Spree. It is similar to the cholera spirillum in shape, has a long terminal flagellum, and is motile.

The colonies which form upon gelatin are circular, have smooth borders, and look very much as if bored out with a tool. They have a brown color and are finely

FIG. 94. Spirillum aquatilis, from an agar-agar culture; x 1000 (Itzerott and Niemann).

granular. In gelatin puncture-cultures the growth occurs almost exclusively at the surface.

The agar-agar cultures are similar to those of cholera. Scarcely any development occurs in bouillon. By the growth of the organism sulphuretted hydrogen gas is produced.

The spirillum does not grow at all upon potato.

Günther did not find the organism to be pathogenic. Spirillum Terrigenus.-This species, also discovered by Günther, was secured from earth. It generally occurs in a slightly curved form, but sometimes is spiral. It is actively motile and has a terminal flagellum.

The colonies, which appear in twenty-four hours, are small, structureless, and transparent, and later take on a "fat-drop" appearance.

Upon agar-agar a thin white coating is formed. Milk is coagulated by the growth of the organism. No indol is produced.

The organism does not stain by Gram's method, and is said not to be pathogenic for guinea-pigs or for mice.

CHAPTER VIII.

PNEUMONIA.

THE term pneumonia," while generally understood to refer to the lobar disease particularly designated as croupous pneumonia, is a vague one, really comprehending a variety of conditions quite dissimilar in character. This being true, no one will be surprised to find that a single organism cannot be described as "specific" for them all. Indeed, pneumonia must be considered as a group of diseases, and the various microbes found associated with it must be described successively in connection with the peculiar phase of the disease in which they occur.

I. Lobar or Croupous Pneumonia.-The bacterium, which can be demonstrated in at least 75 per cent. of the cases of lobar pneumonia, which is now almost universally accepted as the cause of the disease, and about whose specificity very few doubts can be raised, is the pneumococcus of Fränkel and Weichselbaum.

Priority of discovery in the case of the pneumococcus seems to be in favor of Sternberg, who as early as 1880 described an identical organism which he secured from his saliva. Curiously enough, Pasteur seems to have captured the same organism, also from saliva, in the same year. The researches of the observers whose names are attached to the organism were not completed until five years later. It is to Fränkel, Telamon, and particularly to Weichselbaum, however, that we are indebted for the discovery of the relation which the organism bears to pneumonia.

The pneumococcus should rather be called the pneumobacillus, for it habitually has an elongated form, and in its most typical form is so distinctly elongate as to be

described as lanceolate. However, popular parlance has now made it almost impossible to introduce Bacillus pneumoniæ instead of Diplococcus pneumoniae (Weichselbaum), especially as there is already another organism bearing that name. (See Bacillus pneumonia of Friedländer.) The organism (Fig. 95) is variable in its morphology. When grown in bouillon it is oval, has a pronounced dis

FIG. 95.-Diplococcus pneumoniæ, from the heart's blood of a rabbit; x 1000 (Fränkel and Pfeiffer).

position to occur in pairs, and not infrequently forms chains of five or six members, so that some have been disposed to look upon it as a streptococcus (Gamaléia). In the fibrinous exudate from croupous pneumonia, in the rusty sputum, and in the blood of rabbits and mice. containing them the organisms are arranged in pairs, exhibit a distinct lanceolate shape, the pointed ends generally approximated, and are usually surrounded by a distinct halo or capsule of clear, colorless, homogeneous material, thought by some to be a swollen cell-wall, by