September 23, 1897] 



NA TURE 



509 



is left to itself, after a certain time it begins to effervesce, car- 

 bonic acid is evolved, and lactic acid is formed, which decom- 

 poses the carbonate of lime to form lactate of lime. This lactic 

 acid is formed at the expense of the sugar, which disappears 

 little by little. But what is the cause of this transformation of 

 sugar into lactic acid ? Well, Pasteur showed that the efficient 

 cause of this chemical action was a thin layer of organic matter ; 

 that this layer of organic matter consisted of extremely small 

 moving organisms, which increased in number as the fermenta- 

 tion went on. Their growth it is, then, which produces the 

 phenomenon of the transformation of sugar of milk into lactic 

 icid. If, for example, we take a sugary solution in which all 

 pre-existing germs have been destroyed by heat, no lactic fer- 

 mentation will take place. But if we introduce into this sterile 

 liquid a small quantity of this layer of organic matter, such as 

 can be obtained from any liquid in which normal lactic fermen- 

 tation is taking place, we shall see the lactic acid again form 

 rapidly in the new solution. 



Let us dwell a little on this admirable experiment. Nowa- 

 days it seems to us so extremely simple that we can scarcely 

 perceive its importance. It seems to us now, in 1897, that 

 from all time we must have known that an organic solution 

 when heated was sterile, and that a germ would suffice to 

 render it capable of fermentation. But this is a mere delu- 

 sion. No, a thousand times no ! This great fact of the 

 generation of germs was absolutely unknown before Pasteur, 

 and the method of sterilising liquids, and of their inoculation 

 with spores, was revealed to us by Pasteur. It is the nature 

 of great discoveries that they become popularised in a short 

 time, and thus very quickly become elementary. A first year's 

 medical student knows perfectly that which neither Lavoisier, 

 nor Liebig, nor Fremy, nor any one before Pasteur had been 

 able to perceive. We are always tempted to be ungrateful to 

 great creators, for their creations pass rapidly into the domain of 

 common knowledge. They become so simple that they cease to 

 surprise us. We do not think of being grateful, and we forget 

 the efforts which genius has had to make to wrest the truth from 

 jealous nature. Gentlemen, let us not be ungrateful, let us 

 remember that the recognition of the real cause of all fermenta- 

 tion (the development and germination of organised elements) 

 dates from 1857, and from the celebrated memoir of Pasteur 

 upon lactic fermentation. A new world was then opened to 

 science. 



Nevertheless, this memoir of Pasteur's, containing one of 

 the fundamental discoveries of the century, was not wel- 

 comed as it ought to have been. At first its importance was 

 not understood, and afterwards absurd contradictions were 

 opposed to it. A whole series of beautiful and decisive ex- 

 periments was necessary to prove that there was no such 

 thing as spontaneous generation, and that sterile liquids re- 

 mained sterile indefinitely so long as no germs were introduced 

 into them. Pasteur devoted six years (1857-1863) to the 

 proof of the fundamental fact that " organic liquids do not alter 

 until a living germ is introduced into them, and living germs 

 exist everywhere." 



The Microbic Theory of Disease. 



A great step yet remained to be taken. This was to determine 

 the evolution of these germs, not merely in vitro, but in the 

 living organism. We to whom the idea of parasitism and | 

 microbic infection is now so familiar can scarcely conceive that j 

 it has not always been thus. | 



The microbic theory has become so ordinary, so popular, that I 

 we are tempted to believe that the part played by microbes was i 

 understood even in the limes of Hippocrates ; but I assure you j 

 that in truth this was not the case, and for long enough after 

 Hippocrates the power of microbes was not known. 



Pasteur, to whom, and to Sedillot and Littre, we owe the 

 , (ird "microbe," was the-first also to explain to us in his essay I 

 \\ the silkworm disease, published in 1867, the part they I 

 l)layed in the production of disease. He proved that the bright | 

 corpuscles found in the bodies of diseased silkworms are living 

 germs — a distinct living species, a parasite which can multiply 

 and reproduce itself and disseminate the contagion. 



It was therefore with painful astonishment that I heard Prof. 

 Marshall Ward recently say that the discovery of the part played 

 by micro-organisms in disease was due to Koch, and dated from 

 1876. Now, ten years before this, Pasteur had published his 

 experiments on fJbrine ^nAJlacherie. Davaine had shown the 

 part played by bacteria in anthrax infection, and the idea of 



NO. 1456, VOL. 56] 



infection and of contagion by microbes in the higher animah as 

 well as in the lower had become a commonplace, not indeed in 

 the medical world, but in all laboratories. 



Thus, by successive steps, did the work of Pasteur develop in 

 all its greatness and logic. In the first place, in order to 

 elucidate a chemical problem, he studied tartaric fermentation ; 

 then he was led to study lactic fermentation, and he showed 

 that they were biological phenomena. He then pursued the 

 analysis of this phenomena with all its consequences, and was 

 led to the conception that disease was due to the development 

 of a parasite. 



The normal living being follows out its course of growth 

 without the development of any organic parasite in its tissues or 

 in its humours. But if these humours or tissues happen to lie 

 inoculated with any organism capable of developing, then this 

 small living thing multiplies, the higher organism is infected, 

 and the whole body becomes, as it were, a culture fluid, in which 

 the pathogenic microbe propagates itself, a centre of infection 

 which scatters the disease by sowing the noxious germs where- 

 ever it goes. Thus arose the new conception, profoundly new 

 not only for medicine but for hygiene — Disease is Parasitism. 

 Thenceforth we understood the meaning of the words " infection " 

 and "contagion," previously mysterious. 



It is true that Pasteur did not discover all the microbes of 

 all contagious diseases ; but this is of small moment, since he 

 was the first to discover that infection was a phenomenon of 

 microbial parisitism. All those who after him have proved 

 points of detail, however important or fundamental they may 

 be, have but followed the path traced by the master. Whether 

 they will or not, they are all the pupils of Pasteur, as those 

 who follow the study of chemistry are pupils of Lavoisier. 



The greatest of Pasteur's disciples, Robert Koch, although 

 with some ingratitude he refuses to recognise his master, has 

 only perfected certain points in technique and applied his 

 ingenuity and his perspicacity to the solution of questions which, 

 in spite of their practical importance, are still secondarj'. 

 He has not, in fact, been able to do anything new except upon 

 points of detail ; all that is essential comes from Pasteur 

 himself. 



Need I say that this idea of the microbe, of the parasite,, 

 has become the basis of medicine. If we take up treatises 

 on pathology written before this prodigious revolution, we 

 shall be astonished by the insignificance and the nothing- 

 ness of these very ancient books. Vet they are not really 

 very old ; they are dated 1875 or 1880 ; but as one reads them 

 it seems as though several centuries must have intervened 

 between these venerable writings and modern books. I know 

 an excellent article on tuberculosis written in 1878, before the 

 microbe of tuberculosis had been discovered. Well, this 

 article belongs to another age ; it belongs no longer to 

 medicine, but to the history of medicine, for it swarms with 

 mistakes and incredible errors with regard to pathological 

 anatomy, etiology, prophylaxis, treatment — in fact, from every 

 point of view. 



In ten years medicine has been entirely overturned and re- 

 made. It is being re-made every day. Every day brings some 

 new discovery in matters of detail ; but the great principle is 

 always there, and it must always be attributed to the one 

 initiator. 



This is not all. Another new and great discovery was to 

 be made by Pasteur himself, and to constitute the supreme 

 development, the culminating point, as it were, of his life's 

 work. This is the principle of vaccination. By a scries of 

 researches, admirable for their precision, Pasteur proved that 

 the pathogenic microbe could be attenuated — that is to say, 

 rendered incapable of causing death. But, though this microbe 

 does not cause death, yet it can produce the disease, a disease 

 sometimes so attenuated as to be almost imperceptible. Now 

 the living being which has suffered from this attenuated disease 

 is protected against its more serious forms, and, borrowing the 

 word consecrated by the immortal discovery of jenner, Pasteur 

 said that we have here " vaccination." 



Fermentation, infection, contagion, vaccination ; here in four 

 words we have the work of Pasteur. What more need I say ?" 

 Do not these four words possess, in their simplicity, unequalled 

 eloquence. 



Can any one longer maintain that the progress of medicine is 

 not due to experimental science ? Does not all this knowledge 

 of microbes and of the part which they play in disease imply, 

 immediately and necessarily, immense progress in therapeutics ?" 



