Protective vaccinations 455 



half of the same century this disease caused great ravages in France, 

 especially in Paris, where, according to certain statistics (Haeser), 

 about 14,000 persons died in 1716. 



Variolisation or "inoculation" coming to Europe from the East, 

 had come into extensive use when, at the end of the 18th century, 

 the discovery was made that cow-pox, the varioliform disease of the 

 Bovidae, produced in persons who milked cows suffering from this 

 eruption an immunity against small-pox. This idea, popular in 

 origin, was known to breeders in England, France, Germany, and 

 Holland ; we have thus an indication that this knowledge must date 

 from a fairly distant period. Jenner gave the question a scientific 

 and experimental basis, and it was only after his intervention that 

 vaccination by the contents of the pustules of cow-pox began to 

 spread more generally. During the 19th century an immense amount 

 of material bearing on this question was collected ; we have thus 

 been enabled to attain absolutely exact results, and that in spite of 

 the very imperfect state of our knowledge on the etiology of small- 

 pox and of cow-pox. Long ago Chauveau 1 demonstrated that the 

 virus of these diseases must be organised, because that of the vaccine 

 would not pass through a filter. This organism has been carefully 

 sought, but sought in vain in spite of all improvements in micro- 

 biological methods. It was thought that the cocci so often found in 

 the contents of the vaccinal pustule was the specific micro-organism 

 of cow-pox. Such was the opinion of the illustrious botanist Cohn 2 . 

 It was soon shown, however, that this was not the case. The cocci, 

 principally staphylococci, are " secondary" micro-organisms which may 

 be absent from the vaccine without its losing anything of its action. 

 A search was then made for the micro-organism of the vaccine 

 among the protozoan organisms. L. Pfeiffer 3 announced the dis- 

 covery of a species of vaccinal Amoeba. Guarnieri 4 has even 

 described various stages in the reproduction of this hypothetical 

 parasite ; but Salmon 5 demonstrated, in a work carried out in the [478] 

 Pasteur Institute, that we had here to deal merely with leucocytes 

 which had entered epithelial cells and had there undergone marked 



1 Compt. rend. Acad. d. sc., Paris, 1868, t LXVI, pp. 289, 317, 359. 

 a Virchovfs ArcMv, 1872, Bd. LV, S. 229. 



3 Monatssch.f.prakt.Dermat.j Hamburg, 1887; "Die Protozoen als Krankheits- 

 erreger," Jena, 1891, S. 184. 



4 Arch, per le sc. med., Torino, 1892, t. xvi, p. 403. 



5 Ann.de FInst. Pasteur, Paris, 1897, t. xi, p. 289. 



