460 



NATURE 



[September 9, 1697 



particular had paid special attention to some forms ; but neither 

 he nor his successors can be regarded as having founded a 

 school as Cohn did, and this botanist may fitly be looked upon 

 as the father of bacteriology, the branch of mycology which has 

 since obtained so much diversity. 



It should not be overlooked that the first proof that a specific 

 disease of the higher animals is due to a bacillus, contained in 

 Koch's paper on Anthrax, was published under Cohn's auspices 

 and in his " Beitriige zur Biologic der Pflanzen " in 1876, 

 four years after Schroeter's work from the same laboratory on 

 pigmented bacteria, and that the plate illustrating Koch's paper 

 was in part drawn by Cohn. 



It is of primary importance to recognise this detail of Koch's 

 training under Cohn, because, as I have shown at length else- 

 where, popular misapprehensions as to what bacteriology really 

 consists in have been due to the gradual specialisation into three 

 or four different schools or camps of a study which is primarily 

 a branch of botany ; and, again, it is of importance to observe 

 that the whole of this particular branch of mycology, to which 

 special laboratories and an enormous literature are now devoted, 

 has arisen during the last quarter of a century, and subsequent 

 to the foundation of scientific mycology by De Bary. When we 

 reflect that the nature of parasitic fungi, the actual demonstra- 

 tion of infection by a fungus spore, the transmission of germs 

 by water and air, the meaning and significance of polymorphism, 

 heteroecism, symbiosis, had already been rendered clear in the 

 case of fungi, and that it was by these and studies in fermenta- 

 tion and in the life-history of the fungus Saccharomyces that the 

 way was prepared for the aetiology of bacterial diseases in 

 animals, there should be no doubt as to the mutual bearings of 

 these matters. 



Curiously enough, it was an accident which deflected bac- 

 teriology along lines which have proved so significant for the 

 study of this particular group of minute organisms, that an 

 uninitiated visitor to a modern bacteriological laboratory (which 

 in England, at any rate, is usually attached to the pathological 

 department of a medical school) hardly perceives that he is in 

 a place where the culture of microscopic plants is the chief 

 object — for the primary occupation of a bacteriologist is really, 

 after all, the cultivation of minute organisms by the method of 

 "microscopic gardening," invented by De Bary, Klebs, and 

 Brefeld, whether the medium of culture is a nutritive solution, 

 or solid organic substrata like potato, agar, or gelatine, or the 

 tissues of an animal. 



This accident — I use the word in no disrespectful sense — was 

 Koch's ingenious modification of the use of gelatine as a medium 

 in which to grow bacteria : he hit upon the method of pouring 

 melted gelatine containing distributed germs on to plates, and 

 thus isolating the colonies. 



Pasteur and Cohn had already coped with the difficulty of 

 isolating mixed forms by growing them in special fluids. When 

 a given fluid favoured one form particularly, a small quantity 

 containing this predominant species was put into another flask 

 of the fluid, then a drop from this flask transferred to a third 

 flask, and so on, until the last flasks contained only the success- 

 ful species, the others having been suppressed : these " fractional 

 cultures" were brought to a high state of perfection by the 

 botanist Klebs in 1873. 



Then Brefeld (1872) introduced the method of dilution — i.e. 

 he diluted the liquid containing his spores until each single drop 

 taken contained on the average one spore or none, whence each 

 flask of sterile nutritive solution receiving one drop contained 

 either none or one spore. Brefeld was working with fungi, but 

 Lister — now Lord Lister, and our late President— applied this 

 "dilution method" to his studies of the lactic fermentation in 

 1878, and Naegeli, Miquel, and Duclaux carried it further, the 

 two latter especially having been its chief defenders, and Miquel 

 having employed it up to quite recently. 



Solid media appear to have been first generally used by 

 Schroeter in 1870, when he employed potatoes, cooked and 

 raw, egg-albumen, starch-paste, flesh, &c. Gelatine, which 

 seems to have been first employed by Vittadini in 1852, was 

 certainly used by Brefeld as early as 1874, and even to-day his 

 admirable lecture on " Methoden zur Untersuchung der Pilze " 

 of that date is well worth reading, if only to see how cleverly 

 he obtains a single spore isolated in gelatine under the microscope. 

 Klebs used gelatine methods in 1873. 



We thus see that when Koch proposed his method of pre- 

 paring gelatine plate-cultures in 1881 he instituted, not a new 

 culture-medium, for cultures on solid media, including gelatine, 



NO. 1454, VOL. 56] 



had been in use by botanists for eight or ten years ; nor did he 

 introduce methods for the isolation of spores, for this had been 

 done long before. What he really did was to ensure the isolation 

 of the spores and colonies wholesale, and so facilitate the pre- 

 paration of pure cultures on a large scale, and with great saving 

 of time. 



It was a brilliant idea, and, as has been said, "the Columbus 

 egg of Bacteriology"; but we must not lose sight of the fact 

 j that it turned the current of investigation of bacteria from the 

 j solid and trustworthy ground established by Cohn, Brefeld, and 

 ! De Bary, into a totally new channel, as yet untried. 

 I We must remember that De Bary and Brefeld had aimed at 

 obtaining a single spore, isolated under the microscope, and 

 I tracing its behaviour from germination, continuously to the pro- 

 j duction of spores again ; and when we learn how serious were 

 : the errors into which the earlier investigators of the mould-fungi 

 i and yeasts fell, owing to their failure to trace the development 

 j continuously from spore to spore, and the triumphs obtained 

 j afterwards by the methods of pure cultures, it is not difficult to 

 i see how inconclusive and dangerous all inferences as to the mor- 

 ■ phology of such minute organisms as bacteria must be unless 

 I the plant has been so observed. 



As matter of fact, the introduction and gradual specialisation 

 of Koch's methods of rapid isolation of colonies encouraged the 

 very dangers they were primarily intended to avoid. It was 

 soon discovered that pure cultures could be obtained so readily 

 that the characteristic differences of the colonies in the mass 

 could presumably be made use of for diagnostic purposes, and 

 a school of bacteriologists arose who no longer thought it 

 necessary to patiently follow the behaviour of the single spore 

 or bacillus under the microscope, but regarded it as sufficient to 

 describe the form, colour, markings, and physiological changes 

 of the bacterial colonies themselves on and in different media, 

 and were content to remove specimens occasionally, dry and 

 stain them, and describe their forms and sizes as they appeared 

 under these conditions. 



To the botanist, and from the points of view of scientific 

 morphology, this mode of procedure may be compared to what 

 would happen if we were to frame our notions of species of oak 

 or beech according to their behaviour in pure forests, or of a 

 grass or clover according to the appearance of the fields and 

 prairies composed more or less entirely of it, or — and this is a 

 more apt comparison, because we can obtain colonies as pure as 

 those of the bacteriologist — of a mould-fungus according to the 

 shape, size, and colour, &c. , of the patches which grow on bread, 

 jam, gelatine, and so forth. 



Now it is obvious that this is abandoning the methods of 

 morphology, and the consequence has been that two schools of 

 descriptive bacteriologists are working along different lines, and 

 the " species" of the one— the test-tube school— cannot be com- 

 pared with those of the other, the advocates of continuous culture 

 from the spore. 



The difficulty of isolating a bacterium and tracmg its whole 

 life-history under the microscope is so great, that the happy 

 pioneers into the fascinating region opened up by the test-tube 

 methods may certainly claim considerable sympathy in their cry 

 that they cannot wait. Of course they cannot wait ; no amount 

 of argument will prevent the continual description of new test- 

 tube " species," and all we can do is to go on building up the 

 edifice already founded by the botanists Cohn, Brefeld, De Bary, 

 Van Tieghem, Zopf, Prazmowski, Beyerinck, Fischer, and others 

 who have made special studies of bacteria. 



The objection that such work is slow and difficult has no 

 more weight here than in any other department of science, and 

 in any case the test-tube school is already in the plight of being 

 frequently unable to recognise its own " species," as I have con- 

 vinced myself by a long- continued series of cultures with the 

 object of naming common bacteria. 



I wish to guard myself against misconstruction in one par- 

 ticular here. It is not insinuated that the test-tube methods 

 and results are of no value. Far from it ; a vast amount of 

 preliminary information is obtained by it ; but I would insist upon 

 the discouragement of all attempts to make "species" without 

 microscopic culture ; and continuous observation of the develop- 

 ment as far as it can be traced. 



The close connection between bacteriology and medicine has 

 been mainly responsible for the present condition of affairs ; but 

 it is high time we recognised that bacteriology only touches 

 animal pathology at a few points, and that the public learn that, 

 so far from bacteria being synonymous with disease germs, the 



