56 



SCIENCE. 



cause it acts in a certain measure. Vaccination, -then, 

 may be of several degrees ; but we may always succeed 

 in completely vaccinating a chicken, which means that we 

 can bring it to such a condition that it becomes incapable 

 of being affected by the most virulent virus. 



To make this matter clear, I will now give the results 

 of experiments : — I take eighty new chickens (I call new 

 those which never suffered before with chicken cholera). 

 Twenty of these I inoculate with the most virulent virus, 

 and they all die. Of the sixty that remain, I take another 

 lot of twenty, and I inoculate them with that quantity of 

 the most attenuated virus which the point of the needle 

 will take up* — and not one dies. Are they then vacci- 

 nated for the aggravated form of virus ? Some are and 

 some are not, for if I afterwards inoculate these twenty 

 chickens with the most vitulent virus, six or eight of them 

 will not die, although they may be ill, while in the first 

 case every inoculated chicken died. I take again from the 

 remaining chickens another lot of twenty, and these are 

 vaccinated with the attenuated virus exactly as the pre- 

 ceding lot, and, a week afterwards, they are again vac- 

 cinated in the same manner. Are they now safe from the 

 virulent virus? We now inoculate these twenty chickens 

 with this vitulent virus, and, instead of there being six or 

 eight which do not die, there are twelve or filteen. Finally, 

 I take the twenty remaining chickens, and vaccinate 

 them successively three or four times. If now I come to 

 inoculate them with the most virulent virus, not one will 

 die. In this case, chickens are brought to the condition 

 of animals which are incapable of suffering from chicken 

 cholera. 



As to the cause of non-recidivation, I find it impossi- 

 ble to resist the idea that the microscopic germ, which 

 causes the disease, finds in the body of the animal condi- 

 tions suitable to its development, and that to satisfy the 

 necessities of its life, the germ alters certain substances, 

 or destroys them, which comes to the same thing, 

 whether it assimilates them, or whether it consumes 

 them with oxygen borrowed from the blood. 



When complete immunity has been reached, the most 

 virulent germ may be inoculated into any of the mus- 

 cles without producing any effect. This means that 

 the cultivation of the germ has become impossible 

 in these muscles. They no longer contain food for the 

 germ. 



It is impossible to convey the impression that one re- 

 ceives from observing such phenomena. Here are Iwenty 

 chickens which never had this disease. 1 inoculate them 

 in their pectoral muscles or, still better, in the muscle of 

 the thigh, so as to observe with greater ease the effect of 

 the innoculation. The next day all the chickens are 

 lying down ; they are very lame and seem overcome by 

 sleep. The inoculated muscle becomes of enormous size, 

 and is profusely filled with the parasites. From time to 

 time, a chicken dies, and, at the end of forty-e ; ght hours 

 they are all dead. We may take also twenty chickens, 

 previously vaccinated several times, and inoculate them 

 at the same time as the others, with the same virus, in 

 equal quantities. The next day and the next, they are 

 all alive and in good health ; they eat and cackle as 

 usual ; the cocks crow ; the inoculated muscles present 

 nothing abnormal. There is not even a sign to show 

 where the skin was punctured. This healthy condition 

 remains permanent. 



We may now inquire whether the impossibility of cul- 

 tivating the parasite is not limited to the muscles which 

 have been inoculated. This may be answered by intro- 

 ducing the deadly virus in the blood vessels and in the 

 digestive organs. I have taken ten chickens, never before 

 inoculated, and ten others inoculated several times with 

 the mild virus. I have then injected the worst form of 

 virus in the jugular vein of all these chickens. The 



* There arc degrees of attenuation as well as of virulence. I will give 

 explanations in a future communication. 



first ten have died rapidly ; many of them within twenty- 

 four hours. The ten vaccinated chickens, on the con- 

 trary, have only been slightly ill from the incision of the 

 skin and of the jugular vein, and were soon in good 

 health. This shows that the blocd of these ten chickens 

 was itself vaccinated, which means that previous cultiva- 

 tion had deprived it of the materials fit lor further devel- 

 opments of the germ. 



As to the introduction of the parasite in the digestive 

 organs, I have imitated the epidemics which depopulate 

 poultry yards, by introducing the parasite in the food of 

 the chickens. On the nth of March I brought together 

 twelve chickens, bought at the market that very morn- 

 ing, and twelve others, previously vaccinated sevetal 

 times. Every day I gave to these twenty-four chickens 

 a meal of the diseased muscles of chickens, who had died 

 from chicken cholera. Through the combs of the twelve 

 chickens which had not been vaccinated I passed a plati- 

 num wire, so as to distinguish them from the other 

 twelve. On the next day the unvaccinated chickens 

 began to sicken and die. On the 26th of march the ex- 

 periment terminated. Seven of the chickens that had 

 not been vaccinated have died, and a post mortem exam- 

 ination reveals the fact that the disease was introduced 

 in the system, either through the first portion of the ali- 

 mentary canal, or, more frequently, through the bowels, 

 which were highly inflamed, and sometimes ulcerated, in 

 a manner which recalls the lesions of typhoid fever.* 

 The five other unvaccinated chickens are more or less 

 ill, one seriously so. As to the twelve vaccinated 

 chickens, not one has died, and to-day f they are all alive, 

 and in good health. We may now sum up the results as 

 follows : 



It is the life of a parasite, in the interior of the body, 

 which causes the disease known as chicken cholera and 

 which causes death by this disease. When the cultiva- 

 tion of this parasite cannct take place in the body of a 

 chicken, the disease does not show itself. The chicken 

 is then in the constitutional condition of animals which 

 chicken cholera cannot attack. Animals in this condi- 

 tion may be said to be born vaccinnated for this disease, 

 because the foetal evolution has not placed in their bodies 

 the proper food of the parasite, or because substances, 

 which could serve as such food, have disappeared while 

 they were yet young. We must not wonder that there 

 are constitutions more or less apt to receive inoculations 

 of certain kinds of virus, for, as was announced in my 

 first note, the broth of beer-yeast is entirely incapable of 

 supporting the life of the parasite of chicken cholera, 

 while it is well adapted to the cultivation of a multitude 

 of microscopical germs, notably of the bacteridia of 

 carbuncular disease. 



The explanation to which we are led by the facts al- 

 ready mentioned, of the different degrees ol constitutional 

 resistance of some animals, as well as of the immunity 

 which chickens acquire by preventive inoculations, must 

 seem a natural one, if we take into consideration that 

 every cultivation modifies the medium in which it takes 

 place. In the case of ordinary plants, the soil is modi- 

 fied, in the case of parasites, the animals and plants on 

 which they live are also modified. The same thing hap- 

 pens with the liquids in which they live, in the case of 

 ferments and other microscopical germs. The modifica- 

 tions which take place have this character in common, 

 that new cultivations of the same species in these media 

 soon became difficult or impossible. If chicken-broth is 

 used for cultivating the germ of chicken cholera, and if, 

 after three or four days, the liquid is filtered, to separate 

 all the germs, and furthermore, if after this fresh quanti- 

 ties of the germs are placed in the filtered liquid, it will 



* The blood is full of parasites, and the interior organs are frequently 

 covered with pus and false membranes, particularly next to the intestinal 

 pockets, through which the germ seems to have penetrated, 



•I April 26th, 



