with bacilli, an atmosphere containing oxygen is necessary in order for injury to occur. According to Dieudonné, anthrax spores upon agar plates were dead after an exposure to direct sunlight for three and a half hours (bacilli in one and a half hours); if oxygen was excluded, an exposure of nine hours produced no injury.

F. The Activities of Bacteria,

Especially in Regard to the Application of the Same to Diagnostic Purposes.

The activities of bacteria in the test-tube may be designated as: (1) mechanical, (2) optical, (3) thermal, (4) chemical. They will here be discussed in this order; a fifth section will show how the activities of the bacteria enable them to become the causes of disease (pathogenic action).

All the activities of a given variety of bacterium are especially dependent upon, (1) the momentary condition of the bacterium; (2) the nutrient substratum; (3) the entrance of air; (4) the temperature; (5) the illumination.

Since we have already stated what is most important regarding the influence of temperature and light, in the following I must especially discuss the influence of the nutrient medium and the admission of air on one side, and the composition of the final culture on the other. The latter point must always be made especially prominent, in order to show, in the largest possible range, how very much the activity of bacteria changes, according as they are examined when in a full zymogenic, chromogenic, or pathogenic condition, or in an attenuated state.

It is self-evident that to-day a division of bacteria into zymogenic, saprogenic, chromogenic, and pathogenic is not acceptable. Bact. coli causes, for example, in sugar-solutions powerful fermentation; on nutrient media rich in albumin it produces abundant indol and sulphuretted hydrogen; it forms upon potato very often a rather bright brownish-yellow colored layer, and is besides pathogenic for animals and man; it therefore combines the properties of all four groups.

1. MECHANICAL ACTIVITY.

1

Under the microscope we easily observe that many bacteria present pronounced inherent motion, and by study it is found that almost all the motile varieties 1 possess flagella by means of which they propel themselves. The character of the motion is exceedingly variable; for example, creeping (B. megatherium), wabbling (B. subtilis), rolling, snake-like (vibriones); sometimes it is very slow, and sometimes so rapid that any detailed observation can scarcely be made (B. typhi).

In many cases it is difficult to decide whether true active motion is present, or whether the micro-organisms present especially well-marked Brownian or molecular motion-i. e., the dancing and tremor exhibited also by finely divided inorganic particles. In such a case it is recommended to try to render the flagella visible by staining (Technical Appendix), and also to examine the organism in a drop of 5% carbolic acid or 1: 1000 sublimate solution, when, if the motion still persists, we have only to do with molecular motion. Many varieties appear on brief observation to be quiet, but on longer examination single individuals are observed to exhibit positive motion. It seems that the endowments with flagella and motility, when once present, are for the most part reasonably constant peculiarities. Many varieties do not always present motility, it being absent, especially, on many media. According to A. Fischer, with faultlessly developed flagella motion may be absent; for example, in Bac. subtilis on a nutrient medium containing 2% to 4% of ammonium chlorid. We have never observed spontaneous motion or flagella in two different cultures of the Micrococcus agilis AliCohen, obtained from reliable sources and grown upon all ordinary media. We have arrived at the conviction that the same variety may occur either with or without flagella. (Compare special part.)

Th. Smith has described a non-motile form of the mo

1 Upon the actively motile Spirochete Obermeieri and the slowly creeping Beggiatoa no flagella have thus far been demonstrated; therefore the motion is supposed to depend upon a narrow undulating membrane attached to the organism.

tile hog-cholera bacterium; and motile pest cultures and motile bacteria of septicemia hæmorrhagica have been described in isolated instances. Compare also what is said in the special part regarding the Bac. implexus.

As first shown by Pfeffer, many chemical substances actively attract (positive chemotaxis) and others repel bacteria (negative chemotaxis). Oxygen is particularly attractive for aerobic and repellent for anaerobic bacteria. Like Beijerinck, one may obtain very beautiful chemotaxic or aerotaxic figures in the following manner: An unsterilized pea or bean is placed in a test-tube which is threequarters full of sterile water. The bean gives off nutrient materials by diffusion, which slowly extend upward. In this weak nutrient material certain varieties of bacteria introduced with the bean develop at sharply defined horizontal levels, which slowly extend toward the top. Certain varieties form several layers above one another. I have had these interesting statements verified by Mr. Miodowski, and have substantially confirmed them, with the exception that we found a bacterium related to the Bac. mesentericus and the Bac. subtilis predominantly present, instead of the non-sporulating Bac. perlibratus Beij., which Beijerinck found to principally compose the layers. (Compare Beijerinck, C. B. XIV, 827; C. B. L. III, 1; and Miodowski, Dissert. Würzburg, 1896.) In his second work especially, Beijerinck has related a number of interesting observations, but I am unable to enter into details regarding them, nor upon the analogous studies of Jegunow (C. B. L. II).

Schenk has observed a positive thermotropism. If a hanging drop is warmed at one point by a warm wire (temperature difference of 8° to 10°), the bacteria struggle toward it (C. B. XIV, 33).

2. OPTICAL ACTIVITY.

There are found, fairly widely distributed, especially in media rich in salt (sea-water, Elbe, salt-fish), fission fungi which emit light, of which a considerable number, mostly bacteria and vibriones, have been studied. The phosphorescence is a life-symptom of the bacteria and

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does not depend upon oxidation of a photogenic substance separated from the bacteria (K. B. Lehmann and Tollhausen, C. B. v, 785). Everything that interferes with the life of the bacteria, lessens it also; cold makes the organisms rigid, and interrupts the phosphorescence while it continues. High temperature, acids, chloroform, etc., disturb the light-phenomenon momentarily. Living cultures may always be obtained by inoculating from cultures that emit light. The germ-free filtrate never gives light. While no light is given off except when the bacteria are alive, still the live bacteria do not necessarily emit light; for example, in an atmosphere of CO2. Similarly, a muscle can not contract except it is alive, but may be alive without contracting. (Compare also Suchsland, C. B. L. Iv, 713.)

According to Beijerinck (C. B. VIII, 616 and 651), all light-giving bacteria, which he places in a (physiologic) "genus," photobac= terium, require peptone and oxygen in order to emit light. Two of his varieties are satisfied with this; the four others require, besides peptone, also a source for carbon, which may also contain nitrogen. As such, small quantities of sugars (dextrose, levulose, galactose, partly maltose) and glycerin, as also asparagin, are suitable. A higher proportion of sugar, because of marked fermentation and production of acid, stops the emission of light in some cases. As for salts, 3% to 4% of sodium chlorid is favorable, magnesium chlorid appears to promote the production of light still more, while sea-salt is best.

To preserve the photogenic function it is best to employ a gelatin nutrient medium, which is prepared from an infusion of fish in sea-water (or artificial sea-water containing 3% of sea-salt) with the addition of 1% of peptone, 1% glycerin, and 0.5% asparagin. But even on this medium, if the transfer is infrequent, the ability to produce light is soon lost, so that the cultures found in laboratories are not usually photogenic. By repeated frequent transfer to suitable media the photogenic property may often be regained. I employ two salt herrings, cooked in a liter of water, and, after filtering, add 10% gelatin without neutralization.

3. THERMIC ACTIVITY.

The production of warmth during the metabolism of bacteria is absent from our ordinary cultures because of their limited size; even luxuriantly growing, fermenting fluid cultures betray no appreciable warmth to the hand. On the contrary, it is undoubtedly true that the heat exhibited by decomposing organic materials, when stored in a moist condition, as tobacco, hay, manure, etc., depends, at least in part, upon bacterial activity. With the high temperature which thus occurs, the conjecture of Lydia Rabinowitsch, that here the thermophilic bacteria are concerned, seems very probable. Accurate investigations into the causes of these high temperatures are still lacking. (Compare Rabinowitsch, Z. H. xx, 154.)

4. CHEMICAL ACTIVITY.

The chemical activities of bacteria, accompanied partially by the production of light and always by a minimum amount of heat, are to-day, in spite of the very numerous and satisfactory investigations of the last twenty-five years, only known in the roughest outlines. We often know only the principal products, without being accurately informed regarding the mechanism of their origin, the intermediate products, or the bodies occurring in small quantities.

The following three principal varieties of chemical activity may be distinguished:

1. The bacteria elaborate their own body substance. Regarding this the most important points have already been discussed in the proper place.

2. The bacteria secrete ferments, intended to make the nutrient medium in their neighborhood more suitable for assimilation. The products which thus occur in the surroundings of bacteria may be designated as metabolic products.

3. The bacteria assimilate materials and elaborate others which are true metabolic products. It is wrong in principle to make a division into fermentation and metabolic products, as is still sometimes attempted, be