On Vacdnaticn. 



[April, 



person to he infected whh the small-pox P Experience cannot , 

 decide, in the atfirffiative the qaestion when thus btated ; but a ! 

 single observation is sufficient to decide it in the negative. If 

 that observation does not exist, the question must continue 

 jnsohibje ; because, in order to resolve it, we must be acquainted 

 with the nature of the virus of sraali-pox and of cow-pos, with 

 all the circumstances which are capable of excluding or pro- 

 ducing contagion, and with tlie peculiar dispositions which 

 prevent men from contracting it; all of them things absolutely 

 unlmown to us. 



We must therefore confine ourselves to the first - of these 

 questions, and inquire into what confidence we may repose in 

 tiie preservative power of the cow-pox. Such is the nature of 

 the question to be resolved. We thought it necessary to fix its 

 nature with precision, before proceeding to collect, as we have 

 done with the other questions, the positive elements of its solu- 

 tion. Let us establish, in the first place, the nature of the 

 facts which ought fo constitute these elements. 



It is obvious, in the first place, that we ought to exclude all 

 those in which the characters of the cow-pox have not been 

 ascertained. Some persons have considered the difference be- 

 tween the true and false cow-pox as a subtilty ; but we answer^ 

 that when the characters, taken from the epoch of developement 

 of the form and appearance of the pock, of the nature of the 

 humour contained in it, of the manner of its desiccation, and 

 of the mark which remains after it has dropped off, are so distinct 

 from each other, as in the true and false cow-pox : when to 

 this difference is joined the determination of the circumstances 

 upon which the failure of vaccination usually depends, as, for 

 example, the too late period at which the virus has been taken, 

 the changes in the cow-pock which have occasioned the mixture ^ 

 of pus with the true limpid liquor of the cow-pock — when these 

 circumstances have been accurately observed, no farther ambi- 

 guity remains, and the J'stinction between the two kinds of pock 

 is perfectly established^ and may be easily determined.* 



* The facility with which cow-pock matter is altered by carriage, by ex- 

 posure to the asr, by time, and the difficulty of preserving it, are known to 

 every one. When diluted with water it loses its properties sooner. In 

 Rusbia a cold of 0° destroyed Its efiects. In the experiments of Dr. Sacco, 

 > repeated each upon sis children, and by 36 pjincEures, the virus diluted with 

 water at 32^ produced 28 pox; with water from 41 ^ to 86^, 30 pox 5 with 

 *iater at 122*^', only 2; wiih gtEm-water, 30 5 with water containing some 

 ammonia, 30; with saliva, 32. All other mixtures considerably diminished^ 

 or even destroyed the ett'ect. VV^hen 24 punctures were made on ditferent 

 Infants, the matter exposNcd to the air for five hours produced 22 pox ; ex- 

 posed to the air for 24 hours, pox: exposed daring three days, 15 pox. 

 The contact of the other gases diuiinished ihe efficacy of cow-pox matter in five 

 lio'irs ; but it was les^ injured by hydrogen, ammonia, azote, and carbonic 

 acid, than 'ay the others. \ii eSicaey was iutniediately destroyed by nitrau^ 



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