NATURE 



97 



THURSDAY, MAY 29, 1884 



THE DILUTION OF DOG POISON 



M. 



PASTEUR has communicated to the French 

 Academy of Sciences (May 19, 18S4) the results 

 of his experiments on the attenuation of the virus of 

 rabies, which, if they should be confirmed, would furnish 

 us with the means of protecting dogs from rabies, and as 

 a necessary sequel of protecting the human race from 

 hydrophobia, that absolutely deadly and intractable 

 disease which in every country where rabies exists devours 

 every year some hundreds of human victims. 



Starting from the idea, now well established for at least 

 some of the infectious maladies, viz. that the virus of a 

 particular disease of this class on its passage through 

 different species of animals is subject to alteration of its 

 virulence, M. Pasteur inoculated monkeys with the virus 

 taken from a dog affected with rabies, and found that it 

 thereby became considerably altered. This alteration con- 

 sists in a decrease of intensity, and it is the more marked 

 the greater the number of removes. After the third 

 remove {i.e. after having passed successively through 

 three monkeys) it becomes attenuated to such a degree 

 that inoculation with it of dogs, rabbits, and guinea-pigs 

 does not produce fatal rabies. Dogs so inoculated remain 

 protected against further virulent poison such as is 

 derived from a rabid dog. 



But on the other hand the virus of rabies on its passage 

 through the rabbit and guinea-pig increases in virulence, 

 its intensity becoming even greater than that of the virus 

 taken from a dog, rabid in the usual way {rage des rues). 

 The maximum increase in intensity is not, however, 

 attained until several transmissions through the rabbit or 

 guinea-pig. 



In this way it is possible to produce virus of various 

 degrees of intensity, from the weakest, i.e. virus taken 

 from the rabid dog and passed successively through 

 several monkeys, to the strongest, i.e. virus passed suc- 

 cessively through several rabbits or guinea-pigs. 



M. Pasteur states that he has succeeded, by inoculation 

 of the blood of rabid animals, in devising a simple method 

 of obtaining attenuation of the virus, and of herewith 

 protecting dogs from fatal rabies, but the experiments 

 not being yet completed do not permit of a detailed 

 description. 



Without wishing to say anything derogatory as regards 

 these remarkable results, it is greatly to be regretted that 

 M. Pasteur, not being himself a pathologist, has not 

 availed himself of the aid of his medical colleagues, in 

 order to definitely ascertain whether the disease which he 

 produced by inoculation in the dog, monkey, rabbit, and 

 guinea-pig — for this seems to be at the root of his state- 

 ments — was really rabies. However, he has asked and 

 obtained from the French Minister of Public Instruction 

 a Commission which is to compare the results of the 

 inoculation, from a rabid dog, of twenty dogs, previously 

 treated by M. Pasteur with his attenuated virus, with those 

 of the inoculation of twenty other dogs not previously 

 " vaccinated." 



Vol. xxx. — No. 761 



This Commission, comprising such acknowledged 

 authorities in physiology and pathology as M. Bdclard, 

 M. Paul Bert, M. Bouley, Dr. Yillemin, and Dr. Vulpian, 

 will no doubt soon be able to decide this question one way 

 or the other, and its judgment will be awaited by all 

 medical men as well as by the general public with any- 

 thing but indifference. 



The experiments of M. Pasteur, published in the 

 ' Comptes Rendus of the Academy of Sciences for May 19, 

 are these : — 



I. " If rabies is transmitted from the dog to the monkey, 

 and further, from monkey to monkey, the virulence of the 

 virus becomes weakened on each transmission. The 

 virus, having become diminished in virulence by these 

 transmissions from monkey to monkey, if reintroduced 

 into the dog, rabbit, or guinea-pig, maintains its attenuated 

 character. In other words, the virulence does not return 

 at a bound to the virulence of the virus of a dog affected 

 with rabies of the usual kind, i.e. produced by the bite of 

 a dog (tt rage des rues). 



" Under these conditions the attenuation can easily be 

 accomplished by a small number of transmissions from 

 monkey to monkey, to such a point that it does not pro- 

 duce rabies in the dog by hypodermic inoculation. Even 

 inoculation by trephining, an infallible method to com- 

 municate rabies, cannot produce any result ; it creates 

 nevertheless a refractory condition of the animal against 

 rabies. 



II. "The virulence of the rabid virus increases on its 

 passage from rabbit to rabbit, and from guinea-pig to 

 guinea-pig. When in this way the virulence has reached 

 its maximum in the rabbit, it can be transmitted in this 

 state to the dog, and it shows here a much greater in- 

 tensity than the virus obtained from a dog affected with 

 rabies in the usual manner {rage des rues). This virulence 

 is of such an intensity that after inoculation into the blood 

 of a dog it invariably produces fatal rabies. 



III. " Although the virulence increases on the passage 

 of the virus from rabbit to rabbit, or from guinea-pig to 

 guinea-pig, it requires several successive transmissions 

 through these animals to attain its maximum, having pre- 

 viously become attenuated by its passage through the 

 monkey. Similarly the virulence of the ordinary rabies of 

 the dog, which, as we have just shown, is not by any 

 means the greatest that the rabid virus is capable of at- 

 taining, requires several successive transmissions through 

 the rabbit in order to attain its maximum. 



" It follows from the experiments just described that we 

 can easily render dogs proof against rabies. It is readily 

 understood that the experimenter can at will procure rabid 

 virus attenuated in various degrees : some, non-fatal, pro- 

 tecting the animal from the effect of more active as well 

 as of fatal virus. 



" The following example illustrates this : — Extract by 

 trephining from a rabbit dead of rabies after an incuba- 

 tion prolonged by several days beyond the shortest period 

 of incubation in the rabbit. This latter is generally com- 

 prised within seven to eight days after inoculation, by 

 trephining, with the most intensive virus. From the above 

 rabbit, i.e. the one with the prolonged incubation, virus 

 is taken and inoculated, always by trephining, into a 

 second rabbit ; from this again virus is taken and inocu- 

 lated into a third rabbit. Each of these different samples 



