Relation to Oxygen.-Grows better with the admission of oxygen.

Requirements as to Temperature and Nutrient Media. Grows luxuriantly and rapidly at room and incubator temperature upon all nutrient media.

Gelatin Plate.-(a) Natural size: At first, minute white points which liquefy the gelatin as soon as they become a little larger-after twenty-four to forty-eight hours. The older colonies exhibit a small white flake in the center of the liquefied areas; also the edges of the areas present a whitish border (69, VIII).

(b) Magnified fifty times: Young, superficial colonies present a pretty convolution of curly, wavy threads. The center soon becomes dark and cloudy and sinks in, while there remains a row of fine radiating hairs as a peripheral

zone. As the liquefaction advances there is finally a flat, gray saucer, which presents a delicate hairy border toward the solid gelatin, and in the center of which is a curly mass whose structure becomes more and more indistinctly crumbly (69, IX).

Gelatin Stab.-After twenty-four hours there is formed a conical area of liquefaction with whitish flocculi, and at the apex crumbly, yellowish-white masses of bacteria gradually accumulate. After four or five days there forms a grayish, tough pellicle on the surface (69, 1).

Agar Plate.-(a) Natural size. Superficial colonies: White or yellowish white, sharply outlined growths with smooth but irregularly notched borders. The deep colonies remain small, dense, yellowish-white (69, v).

Agar Stab.

Supertains: The center passing mainally into a yel

bem side width & sists of very closely

Ing ies: Roundish, and there presenting single

Ylish-ray to brown,

ad Simy. Gradually it becomes dull, In the stab the growth is After several months the 64, and iv.

Agar Streak.—Lik- the saria & growth of the stab culme. [pend-water of on densation is a tough, wrinkled, brownish pellole Where this passes on to the tube-wall it is pare The water of condensation is clear

Bouillon Culture.-ly on the surface there is a tough, thick, wrinkled pellille, which is firmly adherent to the glass.

Milk Culture. On the surface a dense scum. The milk is not coagulitel, and while the milk becomes transparent. a limited white precipitate is formed.

Potato Culture.-There is rapidly formed an elevated, reddish to grayish-brown, sharply outlined growth. In time the surface develops wavy wrinkles. In old cultures the peripheral zone presents a white, chalky discoloration (69, X).

Spores.-There are no endospores.

Distribution.-Found by Bizozzero upon the skin of healthy men.

Related Varieties.-This variety resembles in many points the subtilis-mesentericus group. Wavy growth, vigorous liquefaction, and air hyphæ upon potato are observed, in which respects its cultures are very similar to those of the B. subtilis. The variety is more properly called Bacillus epidermidis. To be sure, it must then be taken for granted that accidentally a spore-free form of bacillus is exemplified in this variety.

Regarding the forms designated as "Leptothrix buccalis," which occur frequently in the mouth, especially in deposits on the teeth, little can be said that is satisfactory, since cultures have almost always failed.

Miller (Die Bakterien der Mundhöhle, II. Aufl., Berlin, 1894) appears to have cultivated no leptothrix. He cites the following uncultivated leprothrices, briefly and very insufficiently characterized:

Leptothrix gigantea Miller. Threads fixed at one end, small to very thick, with or without distinct septa. Iodin reaction?

Leptothrix maxima buccalis Miller. Jointed threads 1 to 1.3 μ thick, without iodin reaction.

Bacillus maximus buccalis Miller. Like the preceding, but with iodin reaction. It is not stated why this species is designated bacillus while the former are designated leptothrix.

Leptothrix innominata Miller is said to present slender, 0.5 to 0.8 μ thick, tangled, unsegmented, often wavy or bent threads, which sometimes stain violet with iodin.

Arustamow (C. B. VI, 349) described two unnamed leptothrices of the mouth, cultivated by him, both of which grow at incubator temperature, No. 1 being an exquisite anaerobe, No. 2 an outspoken aerobe. The agar growth corresponds in some measure to that of the L. epidermidis; potato and gelatin growths are not described.

Dobrzyniecki (C. B. XXI, 225) has described in detail a Leptothrix placoides alba, which was successfully cultivated aerobically on gelatin. The growth at first resembled anthrax, and then liquefied. The growth on agar was slow-hard, dense colonies being formed. The organism presents long, jointed threads, with a tendency to form tangles, and it stains blue with iodin and iodid of potassium solution and a little lactic acid. Stains by Gram's method. Is not motile.

Flexner has isolated an interesting organism from a rabbit which died of puerperal infection. It occurs in long threads, is always free of spores, has no motion, and does not branch. It is pathogenic, but very difficult to cultivate outside of the body. He names it Bacillus (Leptothrix?) pyogenes filiformis Flexner (Jour. of Exp. Med., Vol. I, 211, 1896).

Long and rather thick (1 to 5 ) unbranched threads, without membranes, and quiet or with a gliding motion. When fresh, there are in part no partitions, but often numerous very highly refracting bodies may be recognized. The granules consist of sulphur, which may especially be recognized if the threads are previously allowed to dry, and also by their solubility in H,S. In this way also the previously indistinguishable transverse partitions become apparent. According to Winogradsky, the breaking up of

the threads into smaller pieces, which later grow out, is the only method of multiplication. The statements of Zopf regarding other forms in the cycle of development of Beggiatoa are opposed by Winogradsky.

According to the old idea, Beggiatoa formed HS and sulphur from sulphates, and was the cause of HS being present in sulphur springs. According to Winogradsky, on the contrary, it is dependent for its nourishment upon the preexisting HS, which it transforms into sulphur. (See Untersuchungen über Schwefelbakterien, C. B. 11, 590.)

Fig. 25.-Beggiatoa alba Vauch (after Zopf).

If

B. alba is found especially in foul slime and dirty water; also sometimes as isolated individuals in pure water. abundant, they form whitish films.

B. nivea Rabenhorst is recognized in sulphur springs as the principal constituent of the slime in the spring.

B. roseo-persicina. Zopf. (Die Spaltpilze, 3. Aufl.) Bacterium photometricum Engelmann (Pflüg. Arch., Bd. 30, 95). This variety is very striking because of its rose-color. In the cooler parts of the year it spreads widely along the banks of small streams, pools, etc. It is always a sign of

contamination of water, but not specific (perhaps from sulphite wood-pulp factories or the like). According to Winogradsky, Zopf has improperly included in this variety a large number of other rose-colored inhabitants of water. Jegunow (C. B. II, 279) has reported many interesting observations regarding another sulphur bacterium, whose classification is still undetermined, but it most likely belongs to the spirilla.

Crenothrix polyspora. Ferd. Cohn.

(Cohn's Beiträge, Bd. 1, H. 11, 130.)

Long, rigid, unbranched threads, consisting of a single row of low cells, unpigmented, included by a membrane which is very thin at the younger parts of the thread and thick at the older parts. The membrane is a product of the cuticle of the cell. In the membrane is deposited

Fig. 26. Crenothrix polyspora. Cohn.

some iron hydroxid or carbonate, which stains it brown. Sometimes also the membranes for considerable lengths are surrounded by a yellow, ferruginous mass with a luster like oil, so that macroscopic, brownish flakes appear.

The thickness of the threads varies from 1.5 to 5.2 μ, it often being easily recognized that the older part of the