outside the plant. We have here a very interesting case of sym- | unable to attack the cellulose itself. There exist in the mud of biosis as mentioned above. The green plant, however, always keeps the upper hand, restricting the development of the bacteria to the nodules and later absorbing them for its own use. It should be mentioned that different genera require different races of the bacterium for the production of nodules. The important part that these bacteria play in agriculture led to the introduction in Germany of a commercial product (the socalled "nitragin ") consisting of a pure culture of the bacteria, which is to be sprayed over the soil or applied to the seeds before sowing. This material was found at first to have a very uncertain effect, but later experiments in America, and the use of a modified preparation in England, under the direction of Professor Bottomley, have had successful results; it is possible that in the future a preparation of this sort will be widely used. d. The apparent specialization of these bacteria to the leguminous plants has always been a very striking fact, for similar bacterial nodules are known only in two or three cases outside this particular group. However, Professor Bottomley announced at the meeting of the British Association for the Advancement of Science in 1907 that he had succeeded in breaking down this specialization and by a suitable treatment had caused bacteria from FIG. 16. a, root nodule of the lupin, nat. size. (From Woromv.) b, longitudinal section through root and nodule. g, fibro-vascular bundle. w, bacterial tissue. (After Woromv.) d, bacteria from nodule of lupin, normal leguminous nodules to infect other plants such as cereals, tomato, rose, with a marked effect on their growth. If these results are confirmed and the treatment can be worked commercially, the importance to agriculture of the discovery cannot be overestimated; each plant will provide, like the bean and vetch, its own nitrogenous manure, and larger crops will be produced at a decreased cost. bacteria. Another important advance is in our knowledge of the part played by bacteria in the circulation of carbon in nature. The enormous masses of cellulose deposited annually on Cellulose- the earth's surface are, as we know, principally the result of chlorophyll action on the carbon dioxide of the atmosphere decomposed by energy derived from the sun; and although we know little as yet concerning the magnitude of other processes of carbon-assimilation-e.g. by nitrifying bacteria -it is probably comparatively small. Such cellulose is gradually reconverted into water and carbon dioxide, but for some time nothing positive was known as to the agents which thus break up the paper, rags, straw, leaves and wood, &c., accumulating in cesspools, forests, marshes and elsewhere in such abundance. The work of van Tieghem, van Senus, Fribes, Omeliansky and others has now shown that while certain anaerobic bacteria decompose the substance of the middle lamella-chiefly pectin compounds-and thus bring about the isolation of the cellulose fibres when, for instance, flax is steeped or "retted," they are marshes, rivers and cloacae, &c., however, other anaerobic bacteria which decompose cellulose, probably hydrolysing it first and then splitting the products into carbon dioxide and marsh gas. When calcium sulphate is present, the nascent methane induces the formation of calcium carbonate, sulphuretted hydrogen and water. We have thus an explanation of the occurrence of marsh gas and sulphuretted hydrogen in bogs, and it is highly probable that the existence of these gases in the intestines of herbivorous animals is due to similar putrefactive changes in the undigested cellulose remains. Sulphur bacteria. Cohn long ago showed that certain glistening particles observed in the cells of Beggiatoa consist of sulphur, and Winogradsky and Beyerinck have shown that a whole series of sulphur bacteria of the genera Thiothrix, Chromatium, Spirillum, Monas, &c., exist, and play important parts in the circulation of this element in nature, e.g. in marshes, estuaries, sulphur springs, &c. When cellulose bacteria set free FIG. 17-A plate-culture of a bacillus which had been exposed for a period of four hours behind a zinc stencil-plate, in which the letters C and B were cut. The 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. (H. M. W.) marsh gas, the nascent gas reduces sulphates-e.g. gypsumwith liberation of SH,, and it is found that the sulphur bacteria thrive under such conditions by oxidizing the SH, and storing the sulphur in their own protoplasm. If the SH, runs short they oxidize the sulphur again to sulphuric acid, which combines with any calcium carbonate present and forms 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 SH, is being set free below by the bacterial decompositions of vegetable mud 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 SH. In the deeper parts of this zone the bacteria absorb the SH2, and, as they rise, oxidize it and store up the sulphur; then ascending into planes more highly oxygenated, oxidize the sulphur to SO,. These bacteria therefore employ SH, as their respiratory substance, much as higher plants employ carbohydrates-instead of liberating energy as heat by the respiratory combustion of sugars, they do it by oxidizing hydrogen sulphide. Beyerinck has shown that Spirillum desulphuricans, a definite anaerobic form, attacks and reduces sulphates, thus undoing the work of the sulphur bacteria as certain de-nitrifying bacteria reverse the operations of nitro-bacteria. Here again, therefore, we have sulphur, taken into the higher plants as sulphates, built up into proteids, decomposed by putrefactive bacteria and yielding SH, which the sulphur bacteria oxidize; the resulting sulphur is then again oxidized to SO, and again combined with calcium to gypsum, the cycle being thus complete. broa bacteria. Chalybeate waters, pools in marshes near ironstone, &c., abound in bacteria, some of which belong to the remarkable genera Crenothrix, Cladothrix and Leptothrix, and contain ferric oxide, .e. rust, in their cell-walls. This iron deposit is not merely mechanical but is due to the physiological activity of the organism which, according to Winogradsky, liberates energy by oxidizing ferrous and ferric oxide in its protoplasm-a view not accepted by H. 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 2FeCO +30H,+0= Fe (OH)+2CO2 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 Pigment bacteria. assumed exceptional importance owing to the discovery that Bacteriopurpurin-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.c. 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. The most recent observations of Molisch seem to show that bacteria possessing bacteriopurpurin exhibit a new type of assimilation-the assimilation of organic material under the influence of light. 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 algae. The pigment itself may be soluble in water, as is the case with the blue-green fluorescent body formed by B. pyocyaneus, B. fluorescens 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 redpurple of the sulphur bacteria, and indeed most bacterial pigments, solution in water does not occur, though alcohol extracts the colour readily. Finally, there are a few forms which yield their colour to neither alcohol nor water, e.g. the yellow Micrococcus cereus-flavus and the B. berolinensis. Much work is still necessary before we can estimate the importance of these pigments. Their spectra are only imperfectly known in a few cases, and the bearing of the absorption on the life-history is still a mystery. In many cases the colour-production is dependent on certain definite conditions-temperature, presence of oxygen, nature of the food-medium, &c. Ewart's important discovery that some of these lipochrome pigments occlude Dairy bacteria. A branch of bacteriology which offers numerous problems of importance is that which deals with the organisms so common in milk, butter and cheese. Milk is a medium not only admirably suited to the growth of bacteria, but, as a matter of fact, always contaminated with these organisms in the ordinary course of supply. F. Lafar has stated that 20% of the cows in Germany suffer from tuberculosis, which also affected 17.7% of the cattle slaughtered in Copenhagen between 1891 and 1893, and that one in every thirteen samples of milk examined in Paris, and one in every nineteen in Washington, contained tubercle bacilli. Hence the desirability of sterilizing milk used for domestic purposes becomes imperative. : FIG. 18. A similar preparation to fig. 17, except that two slit-like openings of equal length allowed the light to pass, and that the light was that of the electric arc passed through a quartz prism and casting a powerful spectrum on the plate. The upper slit was covered with glass, the lower with quartz. The bacteria were killed over the clear areas shown. The left-hand boundary of the clear area corresponds to the line F (green end of the blue), and the beginning of the ultra-violet was at the extreme right of the upper (short) area. The lower area of bactericidal action extends much farther to the right, does glass. The red-yellow-green to the left of F were without effect. because the quartz allows more ultra-violet rays to pass than (H. M. W.) No milk is free from bacteria, because the external orifices of the milk-ducts always contain them, but the forms present in the normal fluid are principally those which induce such changes as the souring or "turning" so frequently observed in standing milk (these were examined by Lord Lister as long ago as 18731877, though several other species are now known), and those which bring about the various changes and fermentations in butter and cheese made from it. The presence of foreign germs, which may gain the upper hand and totally destroy the flavours of butter and cheese, has led to the search for those particular forms to which the approved properties are due. A definite bacillus to which the peculiarly fine flavour of certain butters is due, is said to be largely employed in pure cultures in American dairies, and in Denmark certain butters are said to keep fresh much longer owing to the use of pure cultures and the treatment employed to suppress the forms which cause rancidity. Quite distinct is the search for the germs which cause undesirable changes, or "diseases"; and great strides have been made in discovering the bacteria concerned in rendering milk "ropy," butter "oily" and "rancid," &c. Cheese in its numerous forms contains myriads of bacteria, and some of these are now known to be concerned in the various processes of ripening and other changes affecting the product, and although little is known as to the exact part played by any species, practical applications of the discoveries of the decade 1890-1900 have been made, e.g. Edam cheese. The Japanese have cheeses resulting from the bacterial fermentation of boiled Soja beans. Thermophilous bacteria. escent Bacteria and light. That bacterial fermentations are accompanied by the evolution | the art of the vinegar-maker is directed to preventing the of heat is an old experience; but the discovery that the "spon- accomplishment of the last stage. These oxidations are brought taneous" combustion of sterilized cotton-waste does about by the vital activity of several bacteria, of which fournot occur simply if moist and freely exposed to oxygen, Bacterium aceti, B. pasteurianum, B. kützingianum, and B. but results when the washings of fresh waste are added, xylinum-have been thoroughly studied by Hansen and A. has led to clearer proof that the heating of hay-stacks, Brown. It is these bacteria which form the zoogloea of the hops, tobacco and other vegetable products is due to the vital" mother of vinegar," though this film may contain other activity of bacteria and fungi, and is physiologically a conse- organisms as well. The idea that this film of bacteria oxidizes quence of respiratory processes like those in malting. It seems the alcohol beneath by merely condensing atmospheric oxygen fairly established that when the preliminary heating process of in its interstices, after the manner of spongy platinum, has long fermentation is drawing to a close, the cotton, hay, &c., having been given up; but the explanation of the action as an incombeen converted into a highly porous friable and combustible plete combustion, depending on the peculiar respiration of these mass, may then ignite in certain circumstances by the occlusion organisms-much as in the case of nitrifying and sulphur bacteria of oxygen, just as ignition is induced by finely divided metals.—is not clear, though the discovery that the acetic bacteria will not A remarkable point in this connexion has always been the only oxidize alcohol to acetic acid, but further oxidize the latter necessary conclusion that the living bacteria concerned must be to CO, and OH, supports the view that the alcohol is absorbed exposed to temperatures of at least 70° C. in the hot heaps. by the organism and employed as its respirable substance. Apart from the resolution of doubts as to the power of spores Promise of more light on these oxidation fermentations is afforded to withstand such temperatures for long periods, the discoveries by the recent discovery that not only bacteria and fungi, but even of Miquel, Globig and others have shown that there are numerous the living cells of higher plants, contain peculiar enzymes which bacteria which will grow and divide at such temperatures, e.g. possess the remarkable property of" carrying "oxygen-much as B. thermophilus, from sewage, which is quite active at 70° C., it is carried in the sulphuric acid chamber-and which have thereand B. Ludwigi and B. ilidzensis, &c., from hot springs, &c. fore been termed oxydases. It is apparently the presence of these The bodies of sea fish, e.g. mackerel and other animals, have oxydases which causes certain wines to change colour and alter long been known to exhibit phosphorescence. This phenomenon in taste when poured from bottle to glass, and so exposed to air. is due to the activity of a whole series of marine Much as the decade from 1880 to 1890 abounded with investigaPhosphor bacteria of various genera, the examination and tions on the reactions of bacteria to heat, so the following decade bacteria. cultivation of which have been successfully carried was remarkable for discoveries regarding the effects out by Cohn, Beyerinck, Fischer and others. The of other forms of radiant energy. The observations cause of the phosphorescence is still a mystery. The suggestion of Downes and Blunt in 1877 left it uncertain whether that it is due to the oxidation of a body excreted by the bacteria the bactericidal effects in broth cultures exposed to solar rays seems answered by the failure to filter off or extract any such were due to thermal action or not. Further investigations, in body. Beyerinck's view that it occurs at the moment peptones are worked up into the protoplasm cannot be regarded as proved, and the same must be said of the suggestion that the phosphorescence is due to the oxidation of phosphoretted hydrogen. The conditions of phosphorescence are, the presence of free oxygen, and, generally, a relatively low temperature, together with a medium containing sodium chloride, and peptones, but little or no carbohydrates. Considerable differences occur in these latter respects, however, and interesting results were obtained by Beyerinck with mixtures of species possessing different powers of enzyme action as regards carbohydrates. Thus, a form termed Photobacterium phosphorescens by Beyerinck will absorb maltose, and will become luminous if that sugar is present, whereas P. Pflugeri is indifferent to maltose. If then we prepare densely inseminated plates of these two bacteria in gelatine food-medium to which starch is added as the only carbohydrate, the bacteria grow but do not phosphoresce. If we now streak these plates with an organism, e.g. a yeast, which saccharifies starch, it is possible to tell whether maltose or levulose and fructose are formed; if the former, only those plates containing P. phosphorescens will become luminous; if the latter, only those containing P. Pflugeri. The more recent researches of Molisch have shown that the luminosity of ordinary butcher's meat under appropriate conditions is quite a common occurrence. Thus of samples of meat bought in Prague and kept in a cool room for about two days, luminosity was present in 52% of the samples in the case of beef, 50% for veal, and 39% for liver. If the meat was treated previously with a 3% salt solution, 89% of the samples of beef and 65% of the samples of horseflesh were found to exhibit this phenomenon. The cause of this luminosity is Micrococcus phosphorens, an immotile round, or almost round organism. This organism is quite distinct from that causing the luminosity of marine fish. It has long been known that the production of vinegar depends on the oxidization of the alcohol in wine or beer to acetic acid, the chemical process being probably carried out in two Oxidizing bacteria. stages, viz. the oxidation of the alcohol leading to the formation of aldehyde and water, and the further oxidation of the aldehyde to acetic acid. The process may even go farther, and the acetic acid be oxidized to CO, and OH; FIG. 19.-Ginger-beer plant, showing yeast (Saccharomyces pyriformis) entangled in the meshes of the bacterium (B. vermiforme). (H. M. W.) which Arloing, Buchner, Chmelewski, and others took part, have led to the proof that rays of light alone are quite capable of killing these organisms. The principal questions were satisfactorily settled by Marshall Ward's experiments in 1892-1893, when he showed that even the spores of B. anthracis, which withstand temperatures of 100° C. and upwards, can be killed by exposure to rays of reflected light at temperatures far below anything injurious, or even favourable to growth. He also showed that the bactericidal action takes place in the absence of food materials, thus proving that it is not merely a poisoning effect of the altered medium. The principal experiments also indicate that it is the rays of highest refrangibility-the blue-violet and ultra-violet rays of the spectrum-which bring about the destruction of the organisms (figs. 17, 18). The practical effect of the bactericidal action of solar light is the destruction of enormous quantities of germs in rivers, the atmosphere and other exposed situations, and experiments have shown that it is especially the pathogenic bacteria-anthrax, typhoid, &c.-which thus succumb to lightaction; the discovery that the electric arc is very rich in bactericidal rays led to the hope that it could be used for disinfecting purposes in hospitals, but mechanical difficulties intervene. The recent application of the action of bactericidal rays to the cure of lupus is, however, an extension of the same discovery. Even when the light is not sufficiently intense, or the exposure is too short to kill the spores, the experiments show that attenuation of virulence, Bacteria may result, a point of extreme importance in connexion with the | (though in a different way) as mosquitoes infect man with lighting and ventilation of dwellings, the purification of rivers malaria. If the recent work on the cabbage disease may be and streams, and the general diminution of epidemics in nature. accepted, the bacteria make their entry at the water pores at As we have seen, thermophilous bacteria can grow at high the margins of the leaf, and thence via the glandular cells to the temperatures, and it has long been known that some forms tracheids. Little is known of the mode of action of bacteria on develop on ice. The somewhat different question of these plants, but it may be assumed with great confidence that and cold. the resistance of ripe spores or cells to extremes of they excrete enzymes and poisons (toxins), which diffuse into heat and cold has received attention. Ravenel, the cells and kill them, and that the effects are in principle the Macfadyen and Rowland have shown that several bacilli will same as those of parasitic fungi. Support is found for this bear exposure for seven days to the temperature of liquid air opinion in Beyerinck's discovery that the juices of tobacco (-192° C. to -183° C.) and again grow when put into normal plants affected with the disease known as "leaf mosaic," will conditions. More recent experiments have shown that even ten induce this disease after filtration through porcelain. hours' exposure to the temperature of liquid hydrogen-252° C. (21° on the absolute scale) failed to kill them. It is probable that all these cases of resistance of seeds, spores, &c., are to be connected with the fact that completely dry albumin does not lose its coagulability on heating to 110° C. for some hours, since it is well known that completely ripe spores and dry heat are the conditions of extreme experiments. Pathogealc bacteria. No sharp line can be drawn between pathogenic and nonpathogenic Schizomycetes, and some of the most marked steps in the progress of our modern knowledge of these organisms depend on the discovery that their pathogenicity or virulence can be modified-diminished or increased by definite treatment, and, in the natural course of epidemics, by alterations in the environment. Similarly we are unable to divide Schizomycetes sharply into parasites and saprophytes, since it is well proved that a number of species-facultative parasites-can become one or the other according to circumstances. These facts, and the further knowledge that many bacteria never observed as parasites, or as pathogenic forms, produce toxins or poisons as the result of their decompositions and fermentations of organic substances, have led to important results in the applications of bacteriology to medicine. Bacterial diseases in the higher plants have been described, but the subject requires careful treatment, since several points suggest doubts as to the organism described being the Bacteriosis in plants. cause of the disease referred to their agency. Until recently it was urged that the acid contents of plants explained their immunity from bacterial diseases, but it is now known that many bacteria can flourish in acid media. Another objection was that even if bacteria obtained access through the stomata, they could not penetrate the cell-walls bounding the intercellular spaces, but certain anaerobic forms are known to ferment cellulose, and others possess the power of penetrating the cell-walls of living cells, as the bacteria of Leguminosae first described by Marshall Ward in 1887, and confirmed by Miss Dawson in 1898. On the other hand a long list of plant-diseases has been of late years attributed to bacterial action. Some, e.g. the Sereh disease of the sugar-cane, the slime fluxes of oaks and other trees, are not only very doubtful cases, in which other organisms such as yeasts and fungi play their parts, but it may be regarded as extremely improbable that the bacteria are the primary agents at all; they are doubtless saprophytic forms which have gained access to rotting tissues injured by other agents. Saprophytic bacteria can readily make their way down the dead hypha of an invading fungus, or into the punctures made by insects, and Aphides have been credited with the bacterial infection of carnations, though more recent researches by Woods go to show the correctness of his conclusion that Aphides alone are responsible for the carnation disease. On the other hand, recent investigation has brought to light cases in which bacteria are certainly the primary agents in diseases of plants. The principal features are the stoppage of the vessels and consequent wilting of the shoots; as a rule the cut vessels on transverse sections of the shoots appear brown and choked with a dark yellowish slime in which bacteria may be detected, e.g. cabbages, cucumbers, potatoes, &c. In the carnation disease and in certain diseases of tobacco and other plants the seat of bacterial action appears to be the parenchyma, and it may be that Aphides or other piercing insects infect the plants, much as insects convey pollen from plant to plant, or " In addition to such cases as the kephir and ginger-beer plants (figs. 19, 20), where anaerobic bacteria are associated with yeasts, several interesting examples of symbiosis among bacteria are now known. Bacillus chauvaci ferments cane-sugar solutions in such a way that normal butyric acid, inactive lactic acid, carbon dioxide, and Symbiosis. D h A. One of the brain-like gelatinous masses into which the mature plant" condenses. B. The bacterium with and without its gelatinous sheaths (cf. fig. 19). C. Typical filaments and rodlets in the slimy sheaths. D. Stages of growth of a sheathed filament-a at 9 A.M., bat 3 P.M., cat 9 P.M., dat 11 A.M. next day, e at 3 P.M., fat 9 P.M., gat 10.30 A.M. next day, h at 24 hours later. (H. M. W.) hydrogen result; Micrococcus acidi-paralactici, on the other hand, ferments such solutions to optically active paralactic acid. Nencki showed, however, that if both these organisms occur together, the resulting products contain large quantities of normal butyl alcohol, a substance neither bacterium can produce alone. Other observers have brought forward other cases. Thus neither B. coli nor the B. denitrificans of Burri and Stutzer can reduce nitrates, but if acting together they so completely undo the structure of sodium nitrate that the nitrogen passes off in the free state. Van Senus showed that the concurrence of two bacteria is necessary before his B. amylobacter can ferment cellulose, and the case of mud bacteria which evolve sulphuretted bydrogen below which is utilized by sulphur bacteria above has already been quoted, as also that of Winogradsky's Clostridium pasteurianum, which is anaerobic, and can fix nitrogen only if I will grow over a foot a day, or even common grasses, or asparagus, protected from oxygen by aerobic species. It is very probable that numerous symbiotic fermentations in the soil are due to this co-operation of oxygen-protecting species with anaerobic ones, e.g. Tetanus. Activity of bacteria. Astonishment has been frequently expressed at the powerful activities of bacteria-their rapid growth and dissemination, the extensive and profound decompositions and fermentations induced by them, the resistance of their spores to dessication, heat, &c.-but it is worth while to ask how far these properties are really remarkable when all the data for comparison with other organisms are considered. In the first place, the extremely small size and isolation of the vegetative cells place the protoplasmic contents in peculiarly favourable circumstances for action, and we may safely conclude that, weight for weight and molecule for molecule, the protoplasm of bacteria is brought into contact with the environment at far more points and over a far larger surface than is that of higher organisms, whether-as in plants -it is distributed in thin layers round the sap-vacuoles, or-as in animals-is bathed in fluids brought by special mechanisms to irrigate it. Not only so, the isolation of the cells facilitates the exchange of liquids and gases, the passage in of food materials and out of enzymes and products I of metabolism, and thus each unit of protoplasm obtains opportunities of immediate action, the results of which are re moved with equal To rapidity, not attainable in more complex multiFIG. 21. A plate-culture colony of a species of Bacillus-Proteus (Hauser) cellular organisms. on the fifth day. The flame-like put the matter in another processes and outliers are composed of way, if we could imagine writhing filaments, and the contours all the living cells of a are continually changing while the colony moves as a whole. Slightly large oak or of a horse, magnified. (H. M. W.) having given up the specializations of function impressed on them during evolution and simply carrying out the fundamental functions of nutrition, growth, and multiplication which mark the generalized activities of the bacterial cell, and at the same time rendered as accessible to the environment by isolation and consequent extension of surface, we should doubtless find them exerting changes in the fermentable fluids necessary to their life similar to those exerted by an equal mass of bacteria, and that in proportion to their approximation in size to the latter. Ciliary movements, which undoubtedly contribute in bringing the surface into contact with larger supplies of oxygen and other fluids in unity of time, are not so rapid or so extensive when compared with other standards than the apparent dimensions of the microscopic field. The microscope magnifies the distance traversed as well as the organism, and although a bacterium which covers 9-10 cm. or more in 15 minutes-say o.1 mm. or 100 μ per second-appears to be darting across the field with great velocity, because its own small size-say 5 X 1 μ-comes into comparison, it should be borne in mind that if a mouse 2 in. long only, travelled twenty times its own length, i.e. 40 in., in a second, the distance traversed in 15 minutes at that rate, viz. 1000 yards, would not appear excessive. In a similar way we must be careful, in our wonder at the marvellous rapidity of cell-division and growth of bacteria, that we do not exaggerate the significance of the phenomenon. It takes any ordinary rodlet 30-40 minutes to double its length and divide into two equal daughter cells when growth is at its best; nearer the minimum it may require 3-4 hours or even much longer. It is by no means certain that even the higher rate is greater than that exhibited by a tropical bamboo which during the active period of cell-division, though the phenomenon is here complicated by the phase of extension due to intercalation of water. The enormous extension of surface also facilitates the absorption of energy from the environment, and, to take one case only, it is impossible to doubt that some source of radiant energy must be at the disposal of those prototrophic forms which decompose carbonates and assimilate carbonic acid in the dark and oxidize nitrogen in dry rocky regions where no organic materials are at their disposal, even could they utilize them. It is usually stated that the carbon dioxide molecule is here. FIG. 22.-Portions of a colony such as that in fig. 21, highly magnified, showing the kinds of changes brought about in a few minutes, from A to B, and B to C, by the growth and ciliary movements of the filaments. The arrows show the direction of motion. (H. M. W.) split by means of energy derived from the oxidation of nitrogen, other colourless bacteria. The purple bacteria have thus two AUTHORITIES.-General: Fischer, The Structure and Functions of Bacteria (Oxford, 1900, 2nd ed.), German (Jena, 1903): Migula, System der Bakterien Jena, 1897); and in Engler and Prant!, Die natürlichen Pflanzenfamilien, I. Th. 1 Abt. a; Lafar, Technical Mycology (vol. i. London, 1898); Mace, Traité pratique de bakterio logie (5th ed. 1904). Fossil bacteria: Renault, Recherches sur les Bactériacées fossiles," Ann. des Sc. Nat., 1896, p. 275. Bacteria in Water: Frankland and Marshall Ward. Reports on the Bacteriology of Water." Proc. R. Soc. vol. li. p. 183. vol. liii. p. 245, vol. Ivi. p. 1; Marshall Ward, "On the Biology of B. ramosus," Proc. R. Soc., vol. Iviii. p. 1; and papers on Bacteria of the river Thames in Ann. of Bot. vol. xii. pp. 59 and 287, and vol. xiii. p. 197. Cell-membrane, &c.: Bütschli, Weitere Ausführungen über den Bau der Cyanophyceen und Bakterien (Leipzig, 1896); Fischer, Unters. über den Bau der Cyanophyceen und Bakterien (Jena, 1897); Rowland, "Observations upon the Structure of Bacteria," Trans. Jenner Institute, 2nd ser. 1899, p. 143, with literature. Cilia: Fischer, "Unters. über Bakterien," Pringsh. Jahrb. vol. xxvii.; also the works of Migula and Fischer already cited. Nucleus: Wager in Ann. Bot. vol. ix. p. 659; also Migula and Fischer, l.c.; Vejdovsky, Über den Kern der Bakterien und seine Teilung," Cent. J. Bakt. Abt. II. Bd. xi. (1904) p. 481; ibid." Cytologisches über die Bakterien der Prager Wasserleitung," Cent. f. Bakl. Abt. II. Bd. xv. (1905); Mencl, "Nachträge zu den Strukturverhältnissen yon Bakterium gammari" in Archiv f. Protistenkunde, Bd. viii, (1907), p. 257. Spores, &c.: Marshall Ward, "On the Biology of B. ramosus," Proc. R. Soc., 1895, vol. Iviii. p. 1: Sturgis," A Soil Bacillus of the type of de Bary's B. megatherium," Phil. Trans. |
