apparent injurious influence upon fungi, which remain absolutely undeveloped in an atmosphere of pure CO2 (C. Fränkel, Z. H. v, 332).

Sulphuretted hydrogen appears to be well borne by anaerobes (see above); other varieties are very susceptible to large quantities, as, for example, Bact. Pflügeri (photogenic bacillus) (Lehmann and Tollhausen, C. B. v, 785).

6. INFLUENCE OF TEMPERATURE ON THE LIFE OF BACTERIA.

Every variety of bacterium demands a certain temperature of the nutrient substratum. Vegetative bacterial life is possible from 0° to 70°, some varieties thriving at the upper and some at the lower extreme. For each variety the minimum and maximum temperatures lie about 30° apart, and we may form a comprehensive classification dependent upon the temperature required somewhat as follows:

Psychrophilic bacteria: minimum at 0°, optimum at 15° to 20°, maximum at about 30°. Most water bacteria belong here; for example, many phosphorescent bacteria of the sea. (Compare Forster, C. B. XII, 431.)

Mesophilic bacteria: minimum at 10° to 15°, optimum at 37°, maximum at about 45°. Here belong all varieties pathogenic for man, since one condition for a pathogenic action is an acclimatization to the body temperature.

The B. vulgatus connects this and the following group, as it still grows well at 50°.

Thermophilic bacteria: minimum, 40° to 49°; optimum, 50° to 55°; maximum, 60° to 70°. Here belong many bacteria of the soil, and almost all spore-producing bacilli of the family of B. mesentericus (Globig, Z. H. ш, 294).

More lately Lydia Rabinowitsch has somewhat more closely described eight thermophilic facultative anaerobes, all of which are spore-produc

1Bac. vulgatus thrives, to be sure, from 15° to 50°, a variety of Globig also from 15° to 68°, but such wide intervals of favorable temperature are very rare. Globig found the range of temperature at which thermophilic varieties will develop to be very narrow; for example, he could grow one variety only from 54° to 65°.

ing, non-motile bacilli, whose optimum temperature lies at 60° to 70°, but they still thrive at 34° to 44°, although slowly, and best in anaerobic agar cultures (Z. H. xx, 154). The varieties are widely distributed, especially in feces. She has not undertaken a comparison with the varieties described by previous authors. Other varieties were isolated by Oprescu (A. H. XXXIII, 164). Some of the varieties isolated by Schillinger appear more as abnormally thermotolerant than thermophilic; they grow well at 66°, but better and with fermentation at 37° (H. R., 1898, 568).

By carefully raising and lowering the temperature, Dieudonné (C. B. xvi, 965) was able to increase the range of temperature within which the anthrax bacillus could thrive, at both its upper and lower limits. The anthrax bacillus can gradually become adapted to a temperature of 42°. Pigeons, which, according to the hypothesis of many authors, are fairly immune to ordinary anthrax because of their higher body temperature (42°), die somewhat oftener after inoculation with cultures adapted to higher temperatures. Still more striking were the results when Dieudonné gradually acclimated anthrax bacilli to a temperature of 12°, and found they could still kill frogs kept at 12°.

Temperatures somewhat below the minimum limit the growth, but do not injure the variety concerned. Petruschky has even kept bacteria in an ice-box (about 4° to 6°) as a means of preserving not only the life but also the virulence of certain varieties which rapidly die at higher temperatures. They are first allowed to grow for two days at 20° (streptococci, etc.).

Also temperatures below zero injure bacteria, but do so slowly and with a rapidity varying with different varieties. Individual statements are given in the special part regarding the most important pathogenic varieties.

If temperatures 5° to 10° above the optimum are allowed to operate upon cultures, they are injured in various ways; some show lessened intensity of growth, the virulence and the power of fermentation are reduced, also the ability to form spores is gradually lost. Sometimes the injury is more marked in one direction, sometimes in another.

If the maximum temperature is exceeded, the culture dies, and for the psychrophilic varieties about 37° is quite

rapidly fatal; for the mesophilic, about 60° (Forster); for the thermophilic, 75°. A temperature of 100° is not withstood by any bacterium free of spores for more than a few minutes.

7. MECHANICAL AND ELECTRICAL
INFLUENCES.

In the first edition, at this point I reported the astonishing statements of Meltzer, according to whom short, feeble shaking would operate favorably upon the growth of fluid cultures of bacteria, while more prolonged and more vigorous shaking or long-continued very feeble shaking would operate very unfavorably (Meltzer, Zeit. f. Biol. xxx, p. 464).

Otto Appel, who, at my request, restudied the whole question, arrived at entirely different results. No shaking of longer or shorter duration injured the bacterial growth, except where very severe agitation and the addition of glass pearls caused direct mechanical lesions of the bacteria. Slight shaking, such as cultures experience when placed upon the foundations of strongly working steam-engines, was without effect. (Further communications thereon are found in the Archiv für Hygiene.)

Most of the previously observed effects of the electric current are easily explained as due to the action of heat and electrolysis. Thiele and Wolf demonstrated by means of new investigations, which are not open to objection, that neither the passage of a constant or interrupted current through a culture of bacteria, if electrolysis be avoided, nor the placing of a culture in an interrupted current induction coil, injures the bacteria (C. B. XXV, 650); I. c., also the previous literature, which in part contains remarkable assertions.

8. INFLUENCE OF LIGHT AND RÖNTGEN

RAYS.

The cultures of all bacteria are restricted in their growth by direct sunlight. If the action is more prolonged, they are subsequently less able to grow luxuriantly in the dark, and there results a generation of weakened organisms, shown, for example, by incomplete liquefaction, slight production of pigment, lessened virulence, etc., which only regain their original properties after repeated transplanta

1According to Sternberg the following die at 56°: Streptococcus pyogenes, Bac. anthracis, Bact. mallei, and Vibrio cholera (Amer. Jour. Med. Sciences, July, 1887, 146).

tion on fresh medium in the dark.

With still longer action

of the direct sunlight the micro-organisms die.

Bact. putidum and Bact. prodigiosum were materially disturbed in their ability to produce pigment and trimethylamin by direct sunlight, in July and August in one-half hour and in November in one and a half hours. They grew slowly and prodigiosum liquefied slowly (Dieudonné). Death was produced in these organisms in one and a half and two and a half hours.

Dieudonné (A. G. A. IX, 405 and 537, also an extensive review of literature) has found ultra-violet, violet, and blue light to be very injurious, green but slightly, and red and yellow not at all. On the contrary, Beck and Schultz (Z. H. xxiii, 490), who employed better light-filters, generally observed no injury from the colored light obtained from sunlight. This is to be explained by the slight intensity of the light employed. Also, Beck and Schultz deny that diffuse daylight works injury to bacteria (the chromogenic function is lost in many varieties even when grown in the dark), while Dieudonné asserts:

In diffuse daylight, in spring and summer in three and a half hours and in winter in four and a half hours, there occurs interference with growth, while in from five to six hours death is produced. Electric are light of 900 candle-power checks growth in five hours and kills in eight hours. Incandescent light injures growth in from seven to eight hours, and kills in eleven hours. Similar results occur with Bact. coli, typhi, and B. anthracis. Naturally, Dieudonné's positive results are not disproved by Beck and Schultz's negative ones.

1

For testing the sensitiveness to light, thickly sown gelatin or agar plates are exposed to diffuse or direct sunlight, after the method of H. Buchner, a dark paper cross being placed upon the illuminated side. To exclude the action of heat, one may first carry the light through a layer of water or alum a few centimeters in thickness. After the light has acted for one-half, one, one and a half, two, etc., hours, the plates are placed in a dark room, and it is observed whether the bacteria develop only on the part covered by the cross; in complete death of the exposed bacteria there occurs a sharply outlined cross consisting of the colonies in a clear field.

1 The action of the heat is entirely without interest.

The action of the light seems to occur under the cooperation of the oxygen of the air; obligate anaerobes (tetanus) and facultative aerobes (B. coli), when oxygen is completely excluded, withstand the sunlight very well; for example, B. coli withstood direct intense sunlight for four hours. (Compare also Wesbrook, Journal of Pathology and Bacteriology, iv, 352.)

Regarding the mechanism of the action of light, the observations of Richardson and later of Dieudonné appear important, if not furnishing a complete explanation. They assert that in illuminated agar plates, and indeed only in blue to ultra-violet light, in a short time (even after ten minutes in direct sunlight) peroxid of hydrogen1 appears. For its demonstration one exposes to the light an agar plate, half covered with dark paper, then pours over the same a weak iodid of potassium paste, and upon this a weak solution of ferrous sulphate; the illuminated side becomes dark blue. (With gases that do not contain oxygen there is no formation of H2O2, nor injurious action from light.) This also explains what has been often observed, that one may obtain a slight attenuation of bacilli if they are inoculated upon agar plates that have previously stood in the sunlight. 2 Bacteria previously exposed to light develop especially badly upon media that have been illuminated, much more so than upon good media.

According to Rieder, strong Röntgen rays injure bacterial growth in a way similar to light (Münch. med. Woch., 1898, No. 4, 101).

9. THE EFFECTS ON BACTERIAL GROWTH OF OTHER BACTERIA.

Although it is the endeavor of every bacteriologist to always obtain bacteria in pure culture, we must not forget that in nature bacteria often occur in combination. If

1 With gelatin it is hours before H2O, can be recognized.

Also other decompositions of the nutrient medium by sunlight may occasionally render difficult a subsequent growth of fungi; for example, the origin of formic acid from tartaric acid (Duelaux).