Protective vaccmations 455 



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

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

 ^bout 14,000 persons died in 1716. 



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

 lad 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 

 )rigin, was known to breeders in England, France, Germany, and 

 [olland; we have thus an indication that this knowledge must date 

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

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

 ^Taccination 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^ 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^. 

 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^ announced the dis- 

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

 described various stages in the reproduction of this hypothetical 

 parasite ; but Salmon^ 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. 



''' Vir chow's Archiv, 1872, Bd. lv, S. 229. 



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



crreger," Jena, 1891, S, 184. 



* Arch, per le sc. med., Torino, 1892, t. xvi, p. 40a 

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



