ACUTE INFECTIOUS DISEASES. 

 CHAPTER V. 



COW-POCK VACCINA. 



ETIOLOGY. Vaccina is an excessively infectious disease. The re- 

 markable fact, that, even at the present day, extensive epidemics of 

 small-pox occur in spite of most persons being vaccinated, or even in 

 many cases revaccinated once or oftener, has induced me to make 

 some very careful observations regarding the duration of the protec- 

 tive power of vaccination. I have not yet completed this work, but 

 have gone far enough to satisfy myself that the protection against 

 variola afforded by vaccination is for a far shorter period than is gen- 

 erally believed. 



On the presumption (which is certainly correct) that a person who 

 takes vaccina after vaccination would have taken variola or varioloid if he 

 had been exposed to infection, I have made a large number of observa- 

 tions on revaccination. Through the politeness of Surgeon-General 

 Von Klein and Dr. Von Kottreutter, in Stuttgart, among other cases, 

 I have had the opportunity of following, day by day, the effect of re- 

 vaccination in five hundred recruits. In these cases, where I had per- 

 fect control, I satisfied myself that the number of the recruits in whom 

 normal cow-pocks developed was proportionally small, and corresponded 

 very nearly with the number given by other observers. But it also 

 showed that the number where there was no result was also slight. 

 In most cases, a few days after the vaccination, there were redness and 

 infiltration of the skin, papules, vesicles, etc. Among the latter class, 

 in many cases, eight days after the operation, the inflammation has 

 run its course, and, if the case has not been watched during the inter- 

 val, it would be classed among those where the vaccination had no 

 effect. These inflammations at the point of vaccination may have been 

 the result of the wound from the lancet, and of the foreign body intro- 

 duced under the epidermis through it, or a result of scratching ; but 

 there was also a possibility that it was due to incomplete vaccina run 

 ning a rapid course, and holding the same relation to ordinary vaccina 

 that varioloid does to variola, and which consequently has been called 

 vaccinoid or varioloid-vaccina, in opposition to variola-vaccina. To 

 settle this question, I first vaccinated a number of persons with the 

 contents of blisters and of pustular eruptions. In none of these per- 

 sons was the like result produced. I also revaccinated a number of my 

 pupils and house-patients, in whom, at the first attempt, this modified 

 result had occurred, and in them also the effect failed. These facts 

 make it appear to me very probable that, at the time of a small-pox 

 epidemic, in spite of the common vaccination and revaccination, the 



