LOUIS PASTEUR 311 



year or of different years, and belonging to the most dissimilar canine 

 races. In each case the bulbar portion of the medulla oblongata was 

 taken out from the recently dead animal, triturated and suspended in 

 two or three times its volume of sterilised liquid, making use all along 

 of every precaution to keep our materials pure, and two drops of this 

 liquid injected after trephining into one or two rabbits. The inocula- 

 tion is made with a Pravaz syringe, the needle of which, slightly 

 curved at its extremity, is inserted through the dura-mater into the 

 arachnoid space. The results were as follows : all the rabbits, from 

 whatever sort of dog inoculated, showed a period of incubation which 

 ranged between twelve and fifteen days, without almost a single ex- 

 ception. Never did they show an incubation of eleven, ten, nine, or 

 eight days, never an incubation of several weeks or of several months. 



Dog-rabies, the ordinary rabies, the only known rabies, is thus 

 sensibly one in its virulence, and its modifications, which are very 

 limited, appear to depend solely on the varying aptitude for rabies 

 of the different known races. But we are going now to witness a 

 deep change in the virulence of dog-rabies. 



Let us take one, any one, of our numerous rabbits, inoculated with 

 the virus of an ordinary mad dog, and, after it has died, extract its 

 bulb, prepare it just as described, and inject two drops of the bulb- 

 emulsion into the arachnoid space of a second rabbit, whose bulb will 

 in turn and in time be injected into a third rabbit, the bulb of which 

 again will serve for a fourth rabbit, and so on. 



There will be evidence, even from the first few passages, of a 

 marked tendency towards a lessening of the period of incubation in 

 the succeeding rabbits. Just one example : 



Towards the end of the year 1882 fifteen cows and one bull died 

 of rabies on a farm situated in the neighbourhood of the town of 

 Melun. They had been bitten on October 2 by the farm dog, which 

 had become mad. The head of one of the cows, which had died on 

 November 15, was sent to my laboratory by M. Rossignol, a veteri- 

 nary surgeon in Melun. A number of experiments were made on 

 dogs and rabbits, and showed that the following parts, the only en- 

 cephalic (or those pertaining to the brain) ones tested, were rabid : the 

 bulb, the cerebellum, the frontal lobe, the sphenoidal lobe. The rab- 

 bits trephined and inoculated with those different parts showed the 

 first symptoms of rabies on the seventeenth and eigheenth days after 



