TRANSACTIONS OF SECTION K. 841 



fungi, and that it was by these and studies in fermentation and in the life-history 

 of the fungus Saccharomyces that the way was prepared for the retiology 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 bacteriology 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 micro- 

 scopic 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 ' micro- 

 scopic gardening,' invented by De Bary, Klebs, and Brefeld, whether the medium 

 of culture is a nutritive solution, or solid organic substrata like potato, agar, &r 

 gelatine, or the tissues of an animal. 



This accident — 1 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 successful 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 Methodeti zur Untersuchung der Pike 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 preparing gelatine plate- 

 cultures in 1881 he instituted, not a new culture-medium, for cultures on solid 

 media, including gelatine, had been in use by botanists for eight or ten years ; nor 

 did he introduce methods for the isolation of spores, for this had beeu done long 

 before. What he really did was to ensure the isolation of the spores and colonies 

 wholesale, and so facilitate the preparation 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 Bac- 

 teriology ; ' but we must not lose sight of the fact that it turned the current of 

 investigation of bacteria from the solid and reliable ground established by Cohn, 

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



We must remember that De Bary and Brefeld had aimed at obtaining a single 

 spore, isolated under the microscope, and tracing its behaviour from germination, 

 continuously to the production of spores again ; and when we learn how serious 

 were the errors into which the earlier investigators of the mould-fungi and yeasts 

 fell, owina; to their failure to trace the development continuously from spore to 

 spore, and the triumphs obtained afterwards by the methods of pure cultures, it 

 is not difficult to see how inconclusive and dangerous all inferences as to the mor- 

 phology of such minute organisms as bacteria must be unless the plant has been 

 so observed. 



