ISS Vaccination, [Fm 



contain a pus capable of communicating the same disease by 

 the same means to other patients. 



The inoculation of the cow-pox is not followed by the same 

 phenomena. Commonly at the distance of three days from 

 the inoculation^ and never sooner, when the cow-pock matter 

 is good, but sometimes later, a single pock miikes its appear- 

 ance. In five days time this pock comes to perfection About 

 the eighth day it is surrounded with a red areola which ]§ a 

 little painful. It is at last converted into a blackish brown 

 crust similar t6 that from which the cow-pock matter was 

 taken. Sometimes a slight fever makes its appearance with 

 some swelling of the axillary glands, when the puncture has 

 been made in the arm. The liquid contained in this pustule, 

 if it be taken at the commencement of its formation, is capable, 

 when inoculated, of producing the same phenomena in another 

 person, and this may be continued ad injinitum. 



From what has been said it is evident that the inoculation of 

 the small-pox produces a real small-pox, while that of the cow- 

 pox has not the same result. Hence the matters introduced are 

 not similar. Of course the theory of one of these diseases and of 

 its inoculation cannot be applied to the other. 



The only thing which exists in common between them is that 

 those who have been inoculated by either are henceforth free from 

 all danger of catching the infection of the small-pox This pro- 

 perty, common to the man who has had the small-pox, either 

 naturally or by inoculation, or who has been vaccinated, indi- 

 cates that a general change has been produced in the whole state 

 of the body, which in all of these cases produces a similar result. 

 This result establishes a difference between the person who has 

 been subjected to these processes and him who has not. The 

 latter is exposed to the infection of small-pox^ the former is freed 

 from it. 



What is the nature of this difference no body knows ; experi- 

 ence alone proves its reality. Experience only can in like man- 

 ner decide whether a general irruption be necessary, and whether 

 there be any danger when this eruption does not take place. For 

 it is not by theory that such a question can be decided, but solely 

 by a comparison of facts. If the cow-pock matter introduced 

 under the epidermis not only produces the phenomena which 

 have been mentioned above, but likewise leaves a poison in the 

 system which may occasion different severe diseases, observation 

 ought to prove that it does so. Thus the question when properly 

 stated turns out to be merely a question about a matter of fact. 



But even when we trust solely to experience and observation, 

 the multitude of circumstances often inappreciable, which may in 

 medicine concur to the same result^ and the difficulty of assign* 



