THE GERM THEORY. 803 



the deposit has first been shaken up. Strange to say, the latter ten 

 fowls will die as quickly, and with the same symptoms, as the former 

 ten ; the blood of all will be found to contain after death the same 

 minute infectious organisms. This equality, so to speak, in the viru- 

 lence both of the culture preparation and of the blood is due to an ap- 

 parently futile circumstance. I have made a hundred culture prepara- 

 tions at least, I have understood that this was done without leaving 

 any considerable interval between 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 hundredth 

 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 viru- 

 lence of the successive cultures, a great change will be observed. It 

 will be readily seen, from an inoculation of a series of ten fowls, that 

 the virulence of one culture differs from that of the blood, and from 

 that of a preceding culture, when a sufficiently long interval elapses 

 between the impregnation of one culture with the microbe of the pre- 

 ceding. More than that, we may recognize, by this mode of observa- 

 tion, that it is possible to prepare cultures of varying degrees of viru- 

 lence. One preparation will kill eight fowls out of ten, another five 

 out of ten, another one out of ten, another none at all, although the 

 microbe may still be cultivated. In fact, what is no less strange, if 

 you take each of these cultures of attenuated virulence as a point of 

 departure, in the preparation of successive cultures, and without ap- 

 preciable interval in the impregnation, the whole series of these cult- 

 ures will reproduce the attenuated virulence of that which has served 

 as the starting-point. Similarly, where the virulence is null, it pro- 

 duces 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 moi'bid 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 recognized, because the 

 attenuated microbes have almost the bulk, the form, and the appear- 

 ance 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 normal condition. Then the dis- 

 ease has disappeared. When we inoculate with the microbe, the viru- 

 lence of which is null, there is not even local disorder, the naturae 

 medicatrix carries it off at once ; and here, indeed, we see the influ- 

 ence of the resistance of life, since this microbe, the virulence of which 

 is null, multiplies itself. A little further, and we touch the principle 

 of vaccination. When the fowls have been rendered sufficiently ill by 

 the attenuated virus which the vital resistance has arrested in its de- 



