gen, but then without the development of red pigment. It is somewhat pathogenic, inoculated animals dying with toxic symptoms after introduction of large amounts. The name prodigiosus is derived from the fact that the bloody appearance of the so-called miraculous holy wafers is attributed to infection with this microorganism.

17. Among other pigment-producing bacteria characterized only by the color of their cultures may be mentioned the bacillus ruber balticus, bacillus ruber aquatilis, bacillus cæruleus, bacillus pavoninus, bacillus amethystinus.

(b) Nonchromogenic.

18. Bacillus Liquefaciens.-This is one of the most widespread of the water-bacilli. It is an actively motile rod, often joined in short chains of four or more segments. It rapidly liquefies gelatin. In plates it assumes the form of a dish, upon the base of which lies a gray, bacterial mass. In stab-cultures the growth assumes the form of a stocking, with a dilated upper portion. The odor of the culture is highly disagreeable. The bacillus exhibits facultative anaerobiosis. In nutrient media containing nitrates it generates nitrous acid.

The following likewise are included among water-bacteria: 19. Bacillus Liquidis.-This is a short, plump, slightly motile bacillus, which also rapidly liquefies gelatin. In tubes the gray, liquefied gelatin becomes covered with a thin membrane, which sinks to the bottom on agitation.

20. Bacillus Aquatilis.—This is a slender rod, with spontaneous motility. It liquefies gelatin slowly, and according to some observers not at all. It grows in gelatin upon the surface in the form of small, yellowish colonies, and upon potatoes with a scanty yellow deposit.

In the earth and in certain articles of food the following bacteria are always to be found, which are characterized by especial resistance of their spores:

21. Root-bacillus. This is a large, thick bacillus, with rounded extremities, and possessing slight motility. It develops central spores, and growth takes place only in the presence of oxygen. The whitish-gray colonies that form consist of a network of fine, interlacing threads. They liquefy gelatin. In stab-cultures also filaments and processes form, and an appearance results resembling an inverted fir-tree. Upon agar-agar a network forms suggesting the ramifications of the roots of a tree.

22. Bacillus Subtilis (Hay-bacillus).—This is a large, delicate bacillus that often develops into long, straight threads. The bacillus subtilis is a strictly aerobic organism, and it quickly liquefies gelatin. The temperature-optimum is 30° C. (86° F.); the temperature-minimum, 10° C. (50° F.); the temperaturemaximum, 45° C. (113° F.). Upon plates the bright, grayish

white colony appears surrounded by a sparkling crown. Upon agar-agar the growth is peculiar, a stiff, wrinkled, readily detached deposit forming. The hay-bacillus forms central spores, which are somewhat thicker, but considerably shorter than the mother-cells. It is found in the air, water, dust, feces, hay, etc. In order to obtain the organism in pure culture hay is cut up into small pieces, which are covered with water in an Erlenmeyer flask, and exposed to a boiling temperature for fifteen minutes. In this way all of the germs are destroyed, with the exception of the resistant spores of the hay-bacillus. These then grow, and after two or three days they form a superficial membrane upon the hay-infusion.

23. Potato-bacillus (Bacillus Mesentericus).-Three varieties of this microorganism are distinguished: bacillus mesentericus vulgatus, fuscus, and ruber. The last, especially, which im-. parts a rose tint to potatoes upon which it grows, possesses permanent forms of extraordinary resistance, which withstand boiling for from five to six hours. In proportion to the cell the spore is quite large. The cultural peculiarities of the organism resemble those of the hay-bacillus. Upon potatoes the bacillus gives rise to a wrinkled coating. Milk is coagulated and pep

tonized.

24. Bacillus Spinosus.—This is a strictly anaerobic, motile rod. Its colonies in gelatin form iridescent globules, with thornlike processes. Gelatin is liquefied, with the formation of gas. Stab-cultures, before liquefaction takes place, present the appearance of a prickly caterpillar (Lüderitz). The bacillus spinosus grows both at room-temperature and at the temperature of the body. It forms central spores, the rod becoming at the same time spindle-shaped (clostridium). The bacillus is usually found in garden-earth.

II. MICROCOCCI.

1. NOT LIQUEFYING GELATIN.

(a) Chromogenic.

25. Micrococcus Aurantiacus.-This is a round or oval coccus, arranged in groups. The cultures are yellow, slimy, knobshaped, and they do not extend greatly in width.

26. Micrococcus Versicolor.-This is a small coccus, arranged in groups or in pairs. It occurs with extraordinary frequency in the air. The colonies are irregular in shape, with a yellowishgreen color. They exhibit, especially upon gelatin, a motherof-pearl iridescence, and they cause fermentation in nutrient media containing glucose.

(b) Nonchromogenic.

27. Micrococcus Candicans.-This is a round coccus of moderate size. Its most distinctive feature is its growth in gelatin stab-cultures, in which a nail-shaped growth appears, with a porcelain-white, glistening head.

28. Micrococcus Concentricus.-This is characterized by the concentric extension of its colonies upon gelatin-plates and in stab-culture. The colonies present from a whitish-gray to a bluish-gray color, and are superficially serrated. The cocci themselves are small and are arranged like grapes.

29. Micrococcus Rosettaceus.-This is a coccus of moderate size. Its growth is mainly superficial. Roset-like deposits form, with irregular margins. The colonies are grayish-white in color, but darker in the center, up to brown.

30. Micrococcus Aquatilis.-The colonies are round, and possess a mother-of-pearl luster. The margins appear serrated; the color is light gray. Viewed with low powers of the microscope, the colony appears in the form of a berry.

2. LIQUEFYING GELATIN.

(a) Chromogenic.

31. Micrococcus Cremoides.—This is a small coccus, arranged in groups, and giving rise to a cream colored pigment. At first, the colonies upon gelatin are from yellowish-white to brownishgray, granular, circular; while later the discs appear eroded, and they lie in a liquefied excavation.

32. Sarcina Lutea (Yellow Sarcina).—This coccus, strictly aerobic, is arranged in so-called balls of twine. Upon gelatin

plates it forms rounded, slightly granular, yellow colonies. In stab-cultures marked superficial growth takes place. The cultures generate a citron-yellow pigment. Liquefaction occurs quite late; then the clear, liquefied gelatin overlies the citronyellow precipitate. In addition to the yelFig. 87.—Sarcinæ ; x 600 low sarcina there are also white, orange, (Flügge). and red sarcina, which are distinguished from that described only by the difference in color. The varieties of sarcina are present in the air.

33. Micrococcus Agilis (Ali Cohen).-This actively motile organism (flagella), cultivated from drinking-water, grows upon all nutrient media, with the formation of a rose-red pigment. It slowly liquefies gelatin.

(b) Nonchromogenic.

34. Micrococcus Radiatus.-This is a small coccus, without typical arrangement. Upon plates it forms colonies surrounded

by a sparkling crown. In stab-cultures the colonies, likewise, display horizontal radiation. Gelatin is slowly liquefied.

III. VIBRIOS.

Since the great epidemic of cholera at Hamburg in the year 1892, a large number of vibrios more or less closely resembling that of cholera have been described, which have been cultivated in part from river-water, in part from other sources, and of which the most important will be mentioned.

35. Vibrio Aquatilis Günther.-This organism is scarcely to be confounded with the comma-bacillus, on account of its circular, finely granular colonies, with smooth borders, even inde

pendently of the absence of the cholera-red reaction. It at first grew feebly in liquid nutrient media, but as a result of repeated inoculation it acquired, in consequence of adaptation to such media, the property of growing upon bouillon and peptone

water.

36. Vibrio Berolinensis.-This organism, which was cultivated by Neisser (1893) from the water-supply of Berlin, bears a close resemblance to the cholera-bacillus in regard to form and flagella. Upon gelatin-plates the border of the colonies is, however, mostly smooth. The colonies themselves exhibit a much more finely granular appearance than those of the commabacillus. Gelatin is slowly liquefied, and the cholera-red reac

tion appears. Guinea-pigs died after intraperitoneal injection, with precisely the same symptom-complex as appeared after introduction of true comma-bacilli. Similar vibrios have been cultivated from Munich well-water by Weibel; from Peene water, by Löffler; from the harbor of Gröningen, by Fokker; and from the harbor of Altona, by Kiesling; and, further, from the Seine. In forming an opinion as to the identity of these and the following vibrios with the true exciting agents of Asiatic cholera, Pfeiffer's reaction (p. 187) and the agglutination-test must be given preeminent importance. Both tests yield negative results.

37. Vibrio Metschnikoff.-This was first cultivated in an epidemic among fowl, and subsequently from the water of the Spree.

It is somewhat thicker and shorter than the cholera-vibrio, and sometimes almost coccus-shaped. In hanging drop it exhibits active motility. The cultures resemble those of the cholerabacillus, except that liquefaction is more marked. The nitrosoindol reaction appears within twenty-four hours. This vibrio, in contradistinction from that of cholera, is pathogenic for both pigeons and guinea-pigs.

38. Vibrio Gindha.-This organism was cultivated by von Pasquale from well-water in Gindha near Massowah. It is a rather long, slightly curved rod, actively motile (with a single terminal flagellum). It is but slightly pathogenic, and it does not yield the nitroso-indol reaction.

39. Vibrio Lissabon.-This has been cultivated in the course