156
RESEARCHES ON BACTERIA.
it is vascular, and not prosenchymatous. On the other hand, it must be admitted that the vascular tissue in the bundles of existing Lycopodiaceffi is developed from without inwards, and there appears to be no tendency for them to receive additions in the opposite direction. Isoetes, indeed, seems to be a case to the contrary, but the structure of its central axis, which, according to Hofmeister, receives external additions, is many respects so anomalous that it cannot be very far relied upon. Supposing these difficulties removed, the continuous increase of the radiated cylinder by the multiplication of cells in a " cambium" region, formed by the adjacent portions of the primitive stem tissues, would be a simple and satisfactory explanation. [Since what is above stated has been in type Hegelmeier's memoir "On the Morphology of Lycopodium " ('Bot. Zeit.,' 1872, Nos. 44—48) has reached me. He differs in many respects from previous writers and describes an investment to the central axis of delicate and narrow cells external to the Phloem, which he terms the Phloem-sheath (1. c, p. 776). Professor M'Nab has suggested ('Nature,' Feb. 6, 1873, p. 267) that it was by the multiplication of the cells of this sheath that the "exogenous" growth took place in fossil representatives. I think there is good reason for believing that this was the case.1
RESEARCHES on BACTERIA.1
By Dr. FERDINAND COHN.
(With Plate V.) TWENTY years ago Cohn published his first researches On Bacteria. In the interim these organs have attained special importance in Pasteur's theory of fermentations and Hallier's theory of contagious disease; further, they have been the objective point of certain supposed demonstrations of spontaneous generation. Leuwenhoek and 0. F. Miiller already knew Bacteria, but Ehrenberg first distinguished the genera Bacterium, Vibrio, Spirochutta, and Spirillum. Dajardin added somewhat to the systematic knowledge of these forms; but since his time great confusion has been introduced byjthe vague use of names and introduction of new terms. Especially Pasteur, whose researches are greatly lessened in value by want of knowledge, on his part, of the terminology and methods of biology, has made confusion. 1 'Bcitriige ztir Biologie der Pflaiizen,' 2tes Heft, Brcslau, 1872.
RESEARCHES ON' BACTERIA.
157
He speaks with " sovereign will" of" vegetaux cryptogames microscopiques," " Animacules," " Champignons," " Infusoires," "Torulacees, Hacteries, Vibrioniens, Monades," occasionally introducing the varied and undefined names, " Mycoderrna," " Mucor," " Mucedinees," and "levure." Then we have from other writers the terms Microzyma, Bacteridium, Micrococcus, Leptothrix, Mycothrix, Microsporon, Mikrobacterien, Meso-mikrobacterien, Zooglsea, Microsphasra, and Amylobacter. Cohn defines Bacteria as "chlorophyll-free cells of spherical, oblong, or cylindrical form, sometimes twisted or bent, which multiply themselves exclusively by transverse division, and occur either isolated or in cell-families." Bacteria make fluids milky; but if the fluid is of nearly equal refractive index with them—such as serum, lymph, &c.—they remain invisible, except with the microscope. They are not destroyed by potash, ammonia, nor acids, which is due to their dense cell-membrane, as is also their permanence when dead. They divide, by elongation, to double the normal length and subsequent pinching in, so as to form equal parts. Division only occurs longitudinally; branching is quite foreign to their nature. The cells produced by division separate at once (unicellular Bacteria), or remain attached as strings or threads (filamentous Bacteria), In this last state they resemble the alga genus {Leptothrix); but the bright green forms of true Leptothrix must not be confused with these Bacteria. In those distinguished as spherical and staffshaped Bacteria, the cells resulting from division, as a rule, separate at once; but by the swelling up of their cell-membranes they may form a jelly-like mass or colony, which Cohn distinguished, in 1853, as the Zoogl&afoxm. The filamentous and screw Bacteria never form jelly masses. Bacteria frequently form an oily stratum near the surface of a liquid (attracted by oxygen); this is Pasteur's " mucor." They occur in a third condition (a modification of the Zooglcea), as a toughish pellicle, in which the Bacteria are closely packed in rows; this is Pasteur's Mycoderma. A fourth condition is that of the pulverulent precipitate, which they form when they have exhausted the nutriment in a fluid. They are then to be regarded (as in the parallel case of yeast) as in a " resting phase." Most Bacteria present a motile and a motionless condition. The movement is connected with the presence of oxygen. In certainfilamentousBacteria (Bacteridia, auct.) movement has never been observed. Cohn considers it at present undesirable to discuss the limits and transitions of natural species, VOL. XIII.
NEW SER.
L
158
DR. FREDERICK COHN.
form-species, physiological varieties, and races, but indicates a variety of forms whieh appear to have a certain independence. He distinguishes four tribes, viz. 1, Sphaerobacteria; %, Microbacteria j 3, Desmobacteria; 4, Spirobacteria. In SPH^ROBACTERiAwehave one genus, Micrococcus, with species grouped as Zymogenous, Chromogenous, and Pathogenous. Zymogenous (fermentative) are the common M. crepusculum (Monas crepusculum, Ehr.); M. candidus, Colin; and M. urece, Cohn (the ferment of ammoniacal putrescence). Chromogenous are a very interesting series of colour-producing ferments, viz. Micrococcus prodigiosus (Monas prodigiosa, Ehr., the cause of blood-stained bread, &c); M. luteus, Schrceter (in ' Beitrage zur Biologic der Pflanzen,' Breslau, 1872); M. aurantiacus, Schr.; M. chlwinus, Schr.; M. cyaneus, Schr.; M. violaceus, Schr. Pathogenous are— M. vaccines, Cohn; M. diphthericus, Dertel; M. septicus, Klebs ; M. bombycis, Be'champ. This latter group is of the very highest importance, and excessively difficult to study. Other forms are supposed to exist, but have not yet been examined. The second tribe, MICROBACTERIA, also includes but one genus, viz. Bacterium, with the species B. terma (the common Bacterium of putrefaction), Ehr., 1830, Duj.; B. lineola, Ehr., a larger species, common in brooks and open ponds. Then we have also B. wanthinum, Schro't.; and B. syrir cyanum, Schrot., as chromogenous forms, and the interesting B. veruginosurn, Schrot., the ferment of blue-green pus. The filamentous Bacteria, DESMOBACTERIA, include Bacillus and Vibrio (newly defined) ; in the former thefilamentis straight, in the latter undulated. Bacillus has three species—B. subtilis, Ehr.; B. ulna, Kohn ; and B. anthracis, Cohn. The first is the butyric ferment; the second is like it, but larger and coarser; the third is the pathogenous ferment of the diseases known as " the blood" and " malignant pustule/' Vibrio has two species, one larger than the other, distinguished by Cohn as V. rugula and V. serpens. The SPTROBACTERIA include two genera—Spirockaete and Spirillum-* with species, Sp. plicatilis of the former, Sp. tenue, Ehr.; iSp. undula, Cohn; and Sp. volutans, Ehr., of the latter genus. Cohn remarks that Sp. volutans is the giant among Bacteria ; he has detected a fine flagellum at each end of the screw. Ehrenberg appears to have seen this in his Ophidomonas. Fran Liiders asserted the occurrence of a flagellum at one extremity of the common B. termo, but no one has confirmed her. As regards this and other details, Cohn considers that our present microscopic appliances are unsatisfactory ; he looks for further knowledge with an increased
RESEARCHES ON BACTERIA.
159
magnifying power. The chief forms above mentioned are figured in a well-executed plate, which must furnish the basis for all future nomenclature in treating of these highlyimportant and paradoxical organisms, and which we have accordingly reproduced (see PL V, and explanation.) The Bacteria seem all to belong to the vegetable kingdom, since they exhibit direct and near affinities with undoubted Algae. The have nothing to do with the fungi with which they often make their appearance. Cohn quotes and confirms Burden Sanderson's important discovery of the method of separating Bacteria from Torulse, due to the fact that fungispores are air-carried, while Bacteria require a surface or water to transport them. They are classed in the PhycoclaromacKe, near the Oscillarise amd Nostocacese. Though the term putrefaction may be considered as applying to a process occurring in nitrogenous organic matters, similar to the alcoholic fermentation of nitrogen free organic bodies such as sugar, and though Bacteria may be looked on as the active agents in the one just as Torulse are in the other case yet that Bacteria are dependent for their life on highly organized or albuminoid nitrogenous matters is not found to be a fact. Sanderson found that Bacteria multiply in Pasteur's fluid, and used it as a " test-liquid," to ascertain the presence of living Bacteria or their germs in other liquids and substances. Cohn finds that Pasteur's fluid is better in this •ease when the sugar is left out from it. His researches on the nutrition of Bacteria relate only to B. termo. Although die sugar is superfluous, the ash-salts in Pasteur's fluid exert a very striking effect. A 1 per cent, solution of ammonium tartrate alone fails to support Bacterium life; but to the same solution add the proportion of yeast-ash salts, and at once the growth proceeds. Cohn shows, from his experiments, that the ammonia is the source of the nitrogen, whilst the tartaric acid is the source of the carbon for the multiplying Bacteria. Succinic, acetic, and lactic acid, sugar, glycerine, cellulose, but not carbonic acid, may become the source of carbon. Urea and probably nitric acid may replace the ammonia as sources of nitrogen. The Bacteria then (B. termo) resemble green plants in taking up their nitrogen from ammonia compounds, which animals are unable to do. They differ from green plants in not being able to take their carbon from carbonic acid, but requiring carbo-hydrates and their derivatives. Putrescence is not a spontaneous re-arrangement of the molecules of a substance that has lived, following upon the Fe»oval of life, nor is putrescence the result of a spontaneous
160
DK. FREDERICK COHN.
combination of these molecules with the oxygen of the atmosphere. Putrescence is rather a chemical process excited b j the growth of Bacterium termo. Putrescence never arises when the access of Bacteria to a putrescible body is prevented, and when those already present.have been destroyed. In fact, putrescence is a correlative, not of death, as one sometimes thinks, but of life. The relation of Bacteria to the putrescence of albuminoid matters may be one of these four:— 1. The Bacteria may assimilate these substances, as animals do, and break them up into waste products in their own substance. 2. The Bacteria may shed out a peculiar substance, comparable to diastase or pancreatin, which acts so as to break up albuminoids. 3. Or the Bacteria may act as oxygen carriers, and so break up the albuminoids (oxydising ferments. 4. Or as oxygen-stealers, seizing the oxygen of the albuminoids, and so pulling down their complex fabric (reducing ferments). There is no doubt that, as with all protoplasm, whether vegetable or animal, so with that of Btto teria, repair and waste only go on in the presence of oxygen and with excretion of carbonic acid. In the presence of atmospheric oxygen these processes go on rapidly in Bacteria, but by no means does it follow that their putrefactive action is greater; in fact, just as the yeast-fungus reproduces itself less abundantly, but acts more powerfully as a ferment, i. e. converts more sugar into alcohol when growing in the absence of atmospheric air, so may it be with Bacteria, The oxygen has to be got elsewhere than from the atmosphere, and accordingly from the breaking up of organic molecules. Pasteur has already shown that the organisms of the butyric fermentation (Bacillus) multiply in the absence of atmospheric oxygen, and are checked by its presence. The peculiar products of the fermentative action of Bacteria are, however, by no means to be regarded as due to oxydizing or deoxydizing actions effected on albuminoid bodies attacked by them, for this good reason, that these peculiar products make their appearance when Bacteria are nourished only with tartrate of ammonium and ash-salts.. Cohn shows that the peculiar smells of putrescence, indicating the special products of saprogenous Bacteria, are produced under these circumstances. Further, the peculiar colours of the chromogenous Bacteria are abundantly produced in culture experiments of the same kind, i. e. with ammonium tartrate or acetate and yeast ash-salts, and he would infer the same for the peculiar products of pathogenous Bacteria. Hence the internal chemical phenomena of nutrition are the same, whether albuminoid or ammoniacal
RESEARCHES ON BACTERIA.
161
food is supplied to the Bacteria; and since in the cases of green plants and of animals we have no analogy for supposing the Bacteria to be capable of assimilating at one time ammoniacal salts and at another time organic albumen, we must suppose that the Bacteria always'take their nitrogen in an ammoniacal form. We have the preliminary reduction of the albuminoid to an equivalency with the ammoniaral salt to explain. In this consists the essential feature of putrescence—in a splitting of the albuminoid molecule into ammonia and other fluid and gaseous by-products—just as alcoholic fermentation (we want an English equivalent for Gahrung) consists in the splitting of sugar into alcohol and carbonic acid. Dr. Cohn, in this part of his paper, is a little inconsistent, for he shows that in certain pigment Bacteria the pigment is insoluble, and is contained in the Bacterian cells. This leads to the inference that the peculiar saprogenous, chromogenous, and pathogenous products of nil Hacterian growths are evolved tlms internally. But in speaking of the splitting of the albuminoid molecule into ammonia and byproducts as a necessary external work of the Bacteria preceding their assimilation of the nitrogen of the ammonia, he says that the by-products of the splitting may be the very stinking, coloured, and poisonous products which he has before given proof are formed as a result of the assimilation of simple ammonia salts and of subsequent changes in the protoplasm itself of the Bacteria. The by-products of the preliminary breaking-down of the albuminoid molecule cannot, it seems, be identical with the special products of the Bacterium's life, but may be less peculiar gaseous and other bodies, and consequently this external part of the action of the Bacterium may be compared to the breaking up of sugar by Saccharomyces, whilst the Bacterium's internal work (specific products) has no recognised parallel in the case of yeast. How can we, then, figure to ourselves the power of the Bacteria to split up albuminoid molecules ? Is it a direct function of their vegetation-processes, comparable to the breaking up of carbonic acid in the leaves of green plants under the influence of light? Do the Bacteria act thus " catalytically" as mere excitors or communicators of molecular vibrations, quite innocent of any chemical transference of matter ? Or do they secrete a fluid capable of acting on albuminoids, just as the cells of the alimentary tract secrete digestive juices ? Or is it by the abstraction of oxygen that they upset the albuminoid molecule, as the analogy of yeast suggests? Or, again, is it by bringing condensed oxygen to bear against the complex atom-fabric ? These questions are not yet answered
162
DR. FREDERICK COHN.
But Pasteur's recent generalisation as to the fermentative function of all living cells tends to the third hypothesis. It is exceedingly interesting to note that the disease, " the blood," caused by Bacillus anthracis, is accompanied by all the symptoms of oxygen-starvation and CO2 superloading, and resembles in this way entirely prussic acid poisoning. Pathogenous Bacteria may further, in some cases, produce disease and death by merely diverting nutriment to themselves which should build up the diseased organism. Thirdly, they may produce specific products (comparable to the colour-products of chromogenous forms), which act as diffusible poisons; such is the supposed poison " septicin." The question of the real distinctness and convertibility of the forms and physiologically peculiar species of Bacteria is wisely not yet discussed by Dr. Cohn. Hut he makes the very important remark that it is only in consequence of the recognition of the complete distinctness of pathogenous Bacteria from the commoner Bacteria of putrescence, &c, that the question of contagion has made any advance. So far from being convertible forms or conditions, pathogenous Bacteria are destroyed by the activity of the regular putrefactive Bacteria (B. termo). Cohn, in a large series of experiments, has proved that, practically, a temperature of 80° C. destroys the life of Bacteria, and prevents their development in an organic infusion. Between 65° C. and 80° C. he obtained varying results, which he attributes to the spluttering of the contents of the heated vessels and to the protective influence of solid lumps. In such fluids as Pasteur's a careful heating to 62° C. for one hour was sufficient to prevent development of Bacteria and putrescence. Some doubt seems, however, still to exist as to the butyric ferment—Bacillus subtilis—which in decoctions made with a pea in a tube with ten cub. cent, of water made its appearance sometimes after exposure to temperatures from 60—100° C , the tubes having been closed. Cohn considers that the solid mass of the pea here had effect as a protective, and proves this by a differential experiment; also that Bacillus can withstand higher temperature than can Bacterium. Further, he found that after long boiling no Bacillus nor any Bacteria at all make their appearance. It is this Bacillus which Pasteur believes he obtained in milk after exposure to 105° C. Experiments on the effect of low temperatures have given Cohn the result that Bacteria are not killed by long exposure to cold below 0° C , but they become torpid, Gease mov«ment, growth, and fermentative action, recovering,
ON A NEW ALBA, CltEVOTHUIX POLYSPOR.A.
183
however, these activities with the return of a higher temperature. Dr. Cohn by a mistake cites Professor Frankland, together with Dr. hiastian, as entering the lists on behalf of the " generatio equivoca," and observes that so talented and exact a reasoner as Pasteur has no easy task iu dealing with the French heterogeuists. This is, he says, due not only to the illogical conclusions and the bad experimentation of the supporters of generatio cequivoca, but because there are still, in fact, certain conditions relating to Bacteria which are not fully understood, and which, though he is persuaded they do not directly affect the question at issue, yet render it possible to understand how contradictory statements arise. These conditions are those above noted as to the spluttering of the fluid' aud the protective action of lumps in experiments where putrescible fluids are healed.
On a NEW AI.GA, CRENOTHRIX POLYSPOUA (Cohn), from the WKLL-WATEK of BRESLATJ. By Dr. F. COHN. Trans-
lated in abstract by W. ARCHER, M.R.I.A. WHILST the water-supply of many large towns, both at home and abroad, is, it is to be be feared, not everything that could be wished as regards purity, it is to be hoped that few are so badly off in that respect as, according to Cohn, the town of Breslau appears to be. The greater part of a paper in the first part of his ' Beitrage' a is taken up with an account of the microscopic analysis of samples from various public wells, which revealed all sorts of " abominations." The sample in which the interesting new alga Crenothrix was first met with appears to have come from a part of the town which enjoyed the unenviable reputation of being a " Beriichtigte Typhusgegend," but as this water was full of many sorts of organic matter, living, dying, and dead, we may infer that the Crenothrix was not specially to be accounted a culpable agent in promoting the unhealthy character of the neighbourhood. In this water, which was cloudy, owing to the quantity of Bacteria, Prof. Cohn noticed some little yellowish-brown flakes, of about 1—2 mm. in size, which soon settled to the 1 Dr. Roberts lias snme remarks upon this source of error iu a letter to 'Nature,' Feb. 20th, 1873, p. 302. 2 Cohn: "Ucber den Brunnenfaden (Crenoihrix jioh/spora), mit Bemerkutigen iiber die Mikroskopische Analyse des Brunnenwassers," i n ' Beitrage $ur Biologie der Pilanzeu,' Heft I, p. 108.
