1813.] 



On Vaccination, 



287 



This difference was established in consequence of errors com- 

 mitted in the first eKperiments. At Paris we were in possessiou 

 of the false cow-pock iP.atter, and were not acquainted with the 

 effects of the true till Dr. Woodville made a journey to Fratlce^ 

 and naturalized among us the true matter.* At Geneva false 

 cow-pock matter imposed upou the phj^sicians, and disappointed 

 their hopes during 21 months, till, in May^ 1800, the virus 

 sent by Dr. Pearson succeeded completely. f 



The different characters of the true and faise cow-pock matter 

 have been already [)ointed out in the report inserted in the 5tli 

 volume of the Physical and Mathematical Memoirs of the In- 

 stitute. They have l^een repeatedly published by the central 

 committee of the Society of Paris ; they are described in several 

 f parts of the Bibliotheque Britannique, and in various other 

 publications. Dr. Sacco has given at the end of his work very 

 good plates^ where both the true and the false cow-pock are 

 ' represented. 



Besides this^ Dr. Sacco, endeavouring to fix the time when 

 ' the cow-pox may be usefully communicated, has determined by 



experiment the relation between the probability of success, and 

 , the successive days in whicii the virus has been collected. Ac- 

 f cording to his observations, supposing that the cow-pock begins 



to appear on the third day, as usually happens^ the success may 

 - be considered as certain if the virus be taken between the 5th 

 ! and 8th day, reckoning from tlie tim.e of the puiicture ; or 



■ between the 3d and 6th day, reckoning from the appearance of 

 the pock. He found that when the matter was taken on the 6th 

 day from the appearance of the pock, out of 1 00 punctures, 95 



' succeeded ; when on the "Jih, 92 ; when on the 8th, 88 ; when 

 on the 9th, 85 ; when on the lOth^ 80; when on the 1 1th, 50; 

 and when on the 12th, only from 10 to 15. Besides this, the 

 longer time elapses before the matter be extracted from a pock^ 

 the more likely is the pock to suppurate, and be converted into 



' an ulcer. M. Sacco recommends, likewise, in order to be more 

 certain of the efficacy of the matter, to avoid opening the peck 

 too near the centre where the puncture was made, but to take 



; the matter from as nearly as possible the outer edge of the pock^ 

 where it is more uniformly pure and limpid. Notwithstanding 



■ the various ingenious modes that have been contrived to transport 

 . the matter from one place to another, the most certain method 

 ; of vaccinating, when it can be done, is to take the matter out 

 I; of one arm, and immediately introduce it into another J 



gas, muriatic and oxyraiiriatic acid gases. Light contributed to accelerate th,?' 

 aiferations produced by the air. 



* Report of the Central Committee for 18t33, p. 12, 



+ Bibl. Brit. vol. xiv. p. 19; xv. 76; xvi. 203. 



X M, Voissiii^ physician at Versailles, whose. ZQixl and talenl; have heea 



