SCIENCE. 



421 



the impregnations. Well, here we have the cause of the 

 equality in the virulence. 



"Let us now repeat exactly our successive cultures 

 with this single difference, that we pass from one 

 culture to that which follows it — from the hun- 

 dredth to, say, the hundred and first, at intervals, of 

 a fortnight, a month, two months, three months or 

 ten months. If, now, we compare the virulence of 

 the successive cultures, a great change will be ob- 

 served. It will be readily seen from an inoculation 

 of a series of ten fowls that the virulence of one cul- 

 ture differs from that of the blood and from that of a pre- 

 ceding culture when a sufficiently long interval elapses be- 

 tween the impregnation of one culture with the microbe 

 of the preceding. More than that, we may recognize by 

 this mode of observation that it is possible to prepare cul- 

 tures of varying degrees of virulence. One preparation 

 will kill eight fowls out of ten, another five out of ten, 

 another one out of ten, and another none at all, al- 

 though the microbe may still be cultivated. In fact, what 

 is no less strange, if you take each of these cultures of at- 

 tenuated virulence as a point of departure in the prepara- 

 tion of successive cultures and without appreciable inter- 

 val in the impregnation, the whole series of these culures 

 will reproduce the attenuated virulence of that which has 

 served as the starting point. Similarly, where the virulence 

 is null it produces no effect. How, then, it may be asked, 

 are the effects of these attenuating virulences revealed in 

 the fowls ? They are revealed by a local disorder, by a 

 morbid modification more or less profound in a muscle, if 

 it is a muscle which has been inoculated with the virus. 

 The muscle is filled with microbes which are easily recog- 

 nized, because the attenuated microbes have almost the 

 bulk, the form, and the appearance of the most virulent 

 microbes. 



" But why is not the local disorder followed by death ? 

 For the moment let us answer by a statement of facts. 

 They are these : the local disorder ceases of itself more or 

 less speedily, the microbe is absorbed and digested, if one 

 may say so, and little by little the muscle regains its nor- 

 mal condition. Then the disease has disappeared. When 

 we inoculate with the microbe, the virulence of which is 

 null, there is not even local disorder, the natures medica- 

 trix carries it off at once, and here, indeed, we see the in- 

 fluence of the resistance of life, since this microbe, the 

 virulence of which is null, multiplies itself. A little far- 

 ther, and we touch the principle of vaccination. When 

 the fowls have been rendered sufficiently ill by the atten- 

 uated virus which the vital resistance has arrested in its 

 devt'opment, they will, when inoculated with virulent virus, 

 suffer no evil effects, or only effects of a passing character. 

 In fact, they no longer die from the mortal virus, and tor 

 a time sufficiently long, which in some cases may exceed a 

 year, chicken cholera cannot touch them, especially under 

 the ordinary conditions of contagion which exist in fowl- 

 houses. At this critical point of our manipulation — that 

 is to say, in this interval of time which we have placed be- 

 tween two cultures, and which causes the attenuation — 

 what occurs ? I shall show you that in this interval the 

 agent which intervenes is the oxygen of the air. Nothing 

 more easily admits of proof. Let us produce a culture in 

 a tube containing very little air, and close this tube with 

 an enameller's lamp. The microbe in developing itself, 

 will speedily take all the oxygen of the tube and of the 

 liquid, after which it will be quite free from contact with 

 oxygen. In this case it does not appear that the microbe 

 becomes appreciably attenuated, even after a great lapse 

 of time. The oxygen of the air, then, would seem to be 

 a possible modifying agent of the virulence of the microbe 

 of chicken cholera — that is to say, it may modify more or 

 less facility of its development in the body of animals. 

 May we not be here in presence of a general law appli- 

 cable to all kinds of virus ? What benefits may not be the 

 result ? We may hope to discover in this way the vaccine 

 of all virulent diseases ; and what is more natural than to 



begin our investigation of the vaccine of what we in French 

 call charbon, what you in England call splenic fever, and 

 what in Russia is known as the Siberian pest, and in Ger- 

 many as the Milzbrand. 



" In this new investigation I have had the assistance of 

 two devoted young savants — MM. Chamberland and 

 Roux. At the outset we were met by a difficulty. 

 Among the inferior organisms, all do not resolve them- 

 selves into those corpuscle germs which I was the first 

 to point out as one of the forms of their possible develop- 

 ment. Many infectious microbes do not resolve them- 

 selves in their cultures into corpuscle germs. Such is 

 equally the case with beer yeast which we do not see de- 

 velop itself usually in breweries, for instance, except by 

 a sort of scissiparity. One cell makes two or more, 

 which form themselves in wreaths ; the cells become de- 

 tached, and the process recommences. In these cells 

 real germs are not usually seen. The microbe of chick- 

 en-cholera and many others behave in this way, so much 

 so that the cultures of this microbe, although they may 

 last for months without losing their power of fresh cul- 

 tivation, perish finally like beer yeast which has exhausted 

 all its aliments. The anthracoid microbe iri artificial 

 cultures behaves very differently. In the blood of ani- 

 mals, as in cultures, it is found in translucid filaments 

 more or less segmented. This blood or these cultures 

 freely exposed to air, instead of continuing according to 

 the first mode of generation, show at the end of forty- 

 eight hours corpuscle germs distributed in series more or 

 less regular along the filaments. All around these cor- 

 puscles matter is absorbed, as I have represented it 

 formerly in one of the plates of my work on the diseases 

 of silkworms. Little by little all connection between 

 them disappears, and presently they are reduced to 

 nothing more than germ dust. 



" If you make these corpuscles germinate, the new cul- 

 ture reproduces the virulence peculiar to the thready 

 form which has produced these corpuscles, and this re- 

 sult is seen even after a long exposure of these germs to 

 contact with air. Recently we discovered them in pits 

 in which animals dead of splenic fever had been buried 

 for twelve years, and their culture was as virulent as 

 that from the blood of an animal recently dead. Here I 

 regret extremely to be obliged to shorten my remarks. I 

 should have had much pleasure in demonstrating that 

 the anthracoid germs in the earth of pits in which animals 

 have been buried are brought to the surface by earth- 

 worms, and that in this fact we may find the whole 

 etiology of disease, inasmuch as the animals swallow 

 these germs with their food. A great difficulty presents 

 itself when we attempt to apply our method of attenua- 

 tion by the oxygen of the air to the anthracoid microbes. 

 The virulence establishing itself very quickly, often after 

 twenty-four hours in an anthracoid germ which escapes 

 the action of the air, it was impossible to think of dis- 

 covering the vaccine of splenic fever in the conditions 

 which had yielded that of chicken-cholera. But was 

 there, after all, reason to be discouraged ? Certainly not ; 

 in fact, if you observe closely, vou will find that there is 

 no real difference between the mode of the generation of 

 the anthracoid germ by scission and that of chicken- 

 cholera. We had therefore reason to hope that we 

 might overcome the difficulty which stopped us by en- 

 deavoring to prevent the anthracoid microbe from pro- 

 ducing corpuscle germs, and to keep it in this condition 

 in contact with oxygen for days, and weeks, and months. 

 The experiment fortunately succeeded. 



" In the ineffective {neutre) bouillon de poule the 

 anthracoid microbe is no longer cultivable at 45 C. Its 

 culture, however, is easy at 42 or 43 , but in these con- 

 ditions the microbe yields no spores. Consequently it is 

 possible to maintain in contact with the pure air at 42 

 or 43 a mycclienne culture of bacteria entirely free of 

 germs. Then appear the very remarkable results which 

 I follow. In a month or six weeks the culture dies — that 



