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BACTERIOLOGY 57 and thus bring about the isolation of the cellulose fibres as heat by the respiratory combustion of sugars, they do when, for instance, fiax is steeped or “retted,” they are it by oxidizing hydrogen-sulphide. Beyerinck has shown unable to attack the cellulose itself. There exist in the that Spirillum desulphuricans, a definite anaerobic form, mud of marshes, rivers, and cloacae, &c., however, other attacks and reduces sulphates, thus undoing the work of anaerobic bacteria which decompose cellulose, probably the sulphur bacteria, as certain de-nitrifying bacteria rehydrolysing it first and then splitting the products into verse the operations of nitro-bacteria. Here again therecarbon-dioxide and marsh gas. When calcium sulphate is fore we have sulphur, taken into the higher plants as present, the nascent methane induces the formation of sulphates, built up into proteids, decomposed by putrefaccalcium carbonate, sulphuretted hydrogen, and water. We tive bacteria and yielding SH2 which the sulphur bacteria have thus an explanation of the occurrence of marsh gas oxidize, the resulting sulphur is then again oxidized to and sulphuretted hydrogen in bogs, and it is highly prob- S03 and again combined with calcium to gypsum, the able that the existence of these gases in the intestines of cycle being thus complete. herbivorous animals is due to similar putrefactive changes Chalybeate waters, pools in marshes near ironstone, tire., on the undigested cellulose remains. abound in bacteria, some of which belong to the remarkCohn long ago showed that certain glistening particles able genera Crenothrix, Cladothrix, and Leptoobserved in the cells of Beggiatoa consist of sulphur, and thrix, and contain ferric oxide, i.e., rust, in Iron Winogradsky and Beyerinck have shown that a their cell-walls. This iron deposit is not merely bacteria. ba'fteria whole series of sulphur bacteria of the genera mechanical but is due to the physiological activity of the Thiothrix, Chromatium, Spirillum, Monas, etc., organism which, according to Winogradsky, liberates exist, and. play important parts in the circulation of this energy by oxidizing ferrous and ferric oxide in its proto-element in nature, e.g., in marshes, estuaries, sulphur plasm—a view not accepted by Molisch. The iron must be in certain soluble conditions, however, and the soluble bicarbonate of the protoxide of chalybeate springs seems most favourable ; the hydrocarbonate absorbed by the cells is oxidized, probably thus—

e u ure ^ IG' on dothP!^ '9 ^behind aa bacillus which had inbeen exposed for fourC hours, March, zinc stencil-plate, which the letters and B were cut. 1 lie light had to traverse a screen of water before passing through the C, and one of Aesculin (which filters out the blue and violet rays) before passing the B. The plate was then incubated, and, as the figure shows, the bacteria on the C-shaped area were all killed, whereas they developed elsewhere on the plate (traces of the B are just visible to the right) and covered it with an opaque growth. (Original.)

springs, <fcc. When cellulose bacteria set free marsh gas, the nascent gas reduces sulphates—e.(/., gypsum—with liberation of SH2, and it is found that the sulphur bacteria thrive under such conditions by oxidizing the SH0 and storing the sulphur in their own protoplasm. If the“ SH2 runs short they oxidize the sulphur again to sulphuric acid, which combines with any calcium carbonate present and orms sulphate again. Similarly nascent methane may reduce iron salts, and the black mud in which these bacteria often occur owes its colour to the FeS formed. Beyerinck and Jegunow have shown that some partially anaerobic sulphur bacteria can only exist in strata at a certain depth below the level of quiet waters where SH2 is being set ree below by the bacterial decompositions of vegetable Rmd and rises to meet the atmospheric oxygen coming down from above, and that this zone of physiological activity rises and falls with the variations of partial pressure of the gases due to the rate of evolution of the ee er art s +b e kH QTT2n, and, ^ie ^as Pthey P rise, ' °foxidize this zone absorb it the andbacteria store up the su phur, then ascending into planes more highly oxygenatec oxidize the sulphur to S03. These bacteria therefore employ SH2 as their respiratory substance, much as higher plants employ carbohydrates—instead of liberating energy

2 Fe C03 + 3 OH2 + 0 = Fe2 (OH)6 + 2 C02. The ferric hydroxide accumulates in the sheath, and gradually passes into the more insoluble ferric oxide. These actions are of extreme importance in nature, as their continuation results in the enormous deposits of bog-iron ore, ochre, and—since Molisch has shown that the iron can be replaced by manganese in some bacteria—of manganese ores. Considerable advances in our knowledge of the various chromogenic bacteria have been made by the studies of Beyerinck, Lankester, Engelmann, Ewart, and others, and have assumed exceptional importance bacUril owing to the discovery that Bacterio-purpurin— the red colouring matter contained in certain sulphur bacteria—absorbs certain rays of solar energy, and enables the organism to utilize the energy for its own life-purposes. Engelmann showed, for instance, that these red-purple bacteria collect in the ultra-red, and to a less extent in the orange and green, in bands which agree with the absorption spectrum of the extracted colouring matter. Not only so, but the evident parallelism between this absorption of light and that by the chlorophyll of green plants, is completed by the demonstration that oxygen is set free by these bacteria—i.e., by means of radiant energy trapped by their colour-screens the living cells are in both cases enabled to do work, such as the reduction of highly oxidized compounds. In the case of these red-purple bacteria the colouring matter is contained in the protoplasm of the cell, but in most chromogenic bacteria it occurs as excreted pigment on and between the cells, or is formed by their action in the medium. Ewart has confirmed the principal conclusions concerning these purple, and also the so-called chlorophyll bacteria (B. viride, B. chlorinum, &c.), the results going to show that these are, as many authorities have held, merely minute Algaj. The pigment itself may be soluble in water, as is the case with the blue-green fluorescent body formed by B. pyocyaneus, B. Jluorescens, and a whole group of fluorescent bacteria. Neelson found that the pigment of B. cyanogenus gives a band in the yellow and strong lines at E and F in the solar spectrum—an absorption spectrum almost identical with that of triphenyl-rosaniline. In the case of the scarlet and crimson red pigments of B. prodigiosus, B. ruber, &c., the violet of B. violacens, B. janthinus, &c., the red-purple of the sulphur bacteria, and indeed most S. II. — 8