ON BACTERIOLOGY IN ITS RELATIONS TO CHEMICAL SCIENCE. 451 



of such far-reaching importance that I must ask you to permit me to 

 devote a little further attention to it. There are an immense number of 

 isolated and incidental observations concerning such induced modifi- 

 cations distributed through bacteriological literature, but there are 

 comparatively few connected researches which have been made with the 

 object of deliberately ascertaining what are the limits within which such 

 modifications can be made.^ 



That bacteria are peculiarly liable to present the most extraordinary 

 changes in form was demonstrated already twenty years ago by Professor 

 Ray Lankester's observations on the Beggiafoa roseo-persicina (' Quart. 

 Journ. Mic. Sci.,' xiii. 1873), whilst during recent years the examples of 

 variation, both in form and function, which have been observed are so 

 numerous that even a mere enumeration of them would involve more 

 time than I have at my disposal. It is not, however, perhaps out of 

 place to give those of you who are less familiar with this subject an 

 instance of the profound morphological change which can be impressed 

 on a micro-organism by artificial means. To my mind perhaps the most 

 striking instance of this kind is the artificial production by Chamberland 

 and Roux of a variety of anthrax bacilli, which are incapable of produc- 

 ing spores under any known conditions whatsoever. This fundamental 

 metamorphosis in the morphology and physiology of the organism is 

 eSected by cultivating the ordinary anthrax bacilli in broth, to which a 

 small proportion of potassium dichromate (g^^o), or phenol (about -nrl^K,) 

 has been added. This sporeless, or asporogene, anthrax is equally virulent, 

 and in all respects resembles the ordinary anthrax bacilli, excepting in 

 the particular of inability to form spores. This peculiarity is, moreover, 

 so permanently stamped upon it that it persists even after passing the 

 asporogene bacillus through the bodies of animals. 



I ought also to mention similarly profound and permanent morpho- 

 logical changes which Hansen has made in yeasts by prolonged culture 

 in aerated wort near the maximum temperature. In this manner yeast 

 varieties were obtained which had entirely lost their power of producing 

 spores under whatever conditions they might subsequently be cultivated 

 (Hansen, ' Centralbl. f. Bakteriol.,' vii. [1890], p. 795). 



Equally striking are the changes in the functions of bacteria which can 

 be artificially produced. 



Into the artificial and permanent diminution of the virulence of 

 pathogenic micro-organisms it is not necessary for me to enter, as tho 

 production of attenuated viruses or vaccines for the purposes of preventive 

 inoculation is already carried out on what may be called an industrial 

 scale. But the converse operation may also be eSected, that is to say, an 

 organism possessing only a low degree of virulence may by artificial 

 means have its virulence increased beyond that which it normally 

 exhibits in nature. This has been done by Malm, for the bacillus of 

 anthrax, by passing this organism through animals which, like the dog, 

 are naturally very refractory to this disease, or which have been rendered 

 artificially refractory by vaccination ('Ann. de I'lnst. Pasteur,' vii. [1890], 

 p. 532). Hitherto, however, such increased virulence has not been 



' A useful summary of the principal instances of recorded variations amongst 

 bacteria, more especially those of a pathogenic nature, was contributed to the 

 Pathological Section of the meeting of the British Medical Association, held at 

 Nottingham in July of last year, by Professor Adami (Medical Chronicle, September. 

 1892). 



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