472 Chapter XV 



drops of water. The mixture is filtered through muslin and the fluid 

 dried at 37 C. ; a virulent brown powder is thus obtained. In the 

 preparation of the vaccines a portion of this powder is mixed with 

 water and subjected to a temperature of 100 104 C. for seven 

 hours. Another portion is heated during the same number of hours 

 to 90 94 C. only. This latter forms the second vaccine whilst the 

 first portion constitutes the first. 



In practice the two vaccinal powders are dissolved in cooled boiled 

 water and are introduced into the subcutaneous tissue of the animals 

 that it is wished to immunise. The second vaccine should be injected 

 8 to 12 days after the first. The vaccines are usually tolerated very 

 well by the Bovidae and confer upon them a definite and permanent 

 immunity. In spite of certain drawbacks this method, known as the 

 "Lyons method," has proved to be a very serviceable one and is 

 retained as the best devised up to the present. Its efficacy is 

 proved by the fact that in the period from 1884 to 1895 in 400,000 

 vaccinated animals the mortality has only been 1 per 1 ,000. Arloing, 

 Cornevin, and Thomas thought that raising the virus to a high 

 temperature brought about a real attenuation. 



Leclainche and Vallee 1 , who have recently returned to the study 

 of this question, have shown that this view cannot be maintained. 

 [495] In reality the spores, after being heated to 90 104 C., gave rise to 

 bacilli endowed with their normal and complete virulence. But the 

 heating in the preparation of the Lyons vaccines destroys the toxin 

 manufactured by the Bacillus chauvaei, with the result, that the 

 spores now become the prey of phagocytes : -it is for this reason and 

 for this reason alone that the inoculation of these vaccines is so well 

 tolerated. All the spores of the vaccinal powder are not eaten by the 

 phagocytes : those which are found in the centre of solid particles 

 of the powder ofler a prolonged resistance to the action of the cells, 

 and some of them germinating produce bacilli and give rise to a mild 

 disease capable of conferring immunity. The germination of these 

 spores is further facilitated by the presence of foreign micro- 

 organisms in the vaccinal powders ; these organisms help to interfere 

 with the phagocytosis of the spores of symptomatic anthrax. 



In the course of their researches, Leclainche and Vallee demon- 

 strated that it is easy to vaccinate animals susceptible to anthrax 

 and to confer on them a substantial immunity by means of a single 

 protective injection of a pure culture of Bacillus chauvaei. For this 

 1 Ann. de I'Inst. Pasteur, Paris, 1900, t. xiv, pp. 202, 513. 



