(b) Vibrio serpens.-This is also a septic organism, much thinner and longer than the previous one, more wavy, as a

rule, curved into a single or double wave. The length varies between 0.011 and 0.025 mm. It is motile; and also forms continuous masses, the individuals interlacing in all directions.

NOTE.-Many of the longer pathogenic bacilli, as bacillus of anthrax, of symptomatic charbon, of tubercle, of ulcerative stomatitis, &c., often present themselves in forms closely resembling vibriones.

CHAPTER XIII.

SPIROBACTERIUM (Spirillum).

SPIRILLA are filaments of a spiral shape, motile, and owing to their shape follow a spiral course when moving. They are probably capable of forming minute bright spores.

1. Septic spirilla.-These are found in all kinds of putrefying organic substances, and are of three kinds.

FIG. 94. - SPIRILLUM TENUE, (1) SINGLY AND (2) IN SWARMS (AFTer Cohn).

(a) Spirillum tenue.-This is much finer and more wavy than vibrio serpens, the turns being closer together and spiral. Its length varies between 0·002 and 0·005 mm. ; it often forms continuous felted masses; it is motile.

Occasionally the spirilla grow to a great length-two, three, and more of them forming a chain; the individual spirilla are not arranged in a linear series, but folded into a zigzag. This form, which in reality is not a special kind of spirillum, is

called by Cohn spirocheta plicatilis. The spirillum found in the tartar of the teeth is of this form, spirochæta denticola. But there exist all intermediate forms between a single spirillum tenue and a spirochata. In stained specimens the construction of the spirochata from several spirilla tenua is very distinct.

(b) Spirillum undula is much thicker and shorter than the former; there are all forms between such as are only half a

FIG. 95.-SPIRILLUM UNDULA (AFTER COHN).

FIG. 96.--SPIRILLUM VOLUTANS (AFTER COHN).

turn to such as are of a whole turn of a spiral. It is motile and forms chains of two or more elements, occurring also in continuous masses, occasionally held together by a hyaline interstitial substance.

(c) Spirillum volutans.-These organisms are giant spirilla: long and thick, with granular protoplasm; 0025 to 0.03 mm. long; motile, and with a flagellum at each end.

Beiträge zur Biologie d. Pflanzen, vol. ii.

2. Pigment spirilla.

(a) I have seen on paste a spirillum, morphologically identical with spirillum undula; it is of a pale pink or rosy colour.1 It is motile, and forms a kind of zoogloa, the individuals being closely placed and therefore producing a rosy colour of a more

decided tint. Where they form continuous masses, the naked eye can detect the rosy tint.

(b) Spirillum sanguineum (Ophidomonas sanguinea Ehrenberg). This was observed by Cohn and Warming" in pondwater. Morphologically it is identical with spirillum volutans.

I "On a Rose-coloured Spirillum," Quar. Journ. of Micr. Sci., vol. xv. New Scries.

2 Beitr. 2. Biol. d. Pflanzen, vol. i.

It is motile, with a flagellum either at one or both ends; Warming occasionally saw two and three flagella at one end. It is about 0.003 mm. thick; all forms occur between such as have half and such as have two and a half turns of a spiral. Lankester also saw the same kind of organism amongst his peach-coloured bacteria.1

3. Pathogenic spirilla.

Spirillum Obermeyeri (of relapsing fever) is morphologically identical with spirillum tenue (or spirochata plicatilis of Cohn).

FIGURE.

Blood-corpuscles and spirilla.

Magnifying power 700. (After Koch.)

It was discovered in great numbers by Obermeyer 2 in the blood of the general circulation in patients suffering from

1 Quarterly Journ. of Micr. Science, vol. xiii. New Series.

2 Centralbl. f. med. Wiss. 10, 1573.