VACCINA. 609 



number of persons liable to variola or varioloid is quite large ; and, al- 

 though I have arrived at no conclusion as to the duration of the pro- 

 tective power of vaccina, I think I may still advise physicians to revac- 

 cinate all their patients at the outbreak of an epidemic, no matter what 

 the length of time since their last vaccination. The contents of the 

 vaccina pustule are the only known vehicle of the contagion ; the ema- 

 nations from the skin and lungs, which convey the variola poison, do 

 not carry vaccina poison ; at least, a well person is never infected by 

 entering the atmosphere of a person or beast with vaccina. A second 

 important difference between variola and vaccina poison is, that the 

 latter only induces an eruption at the point where it was introduced, 

 never at remote parts, as the former does. It is not necessary to de- 

 cide the question whether this difference depends on the fact that 

 vaccina poison is of a different nature from variola poison, or whether 

 the latter is weakened by being transferred to another species of ani- 

 mal, being more imperfect and less active when reproduced in the cow. 

 The predisposition to vaccina is very general, and it is rare for a per- 

 son vaccinated for the first time to escape the disease. A single at- 

 tack sometimes removes the liability to the disease for the rest of life ; 

 but, in the majority of cases, this immunity only lasts a number of 

 years, and then ceases. The important discovery, that having had 

 vaccina removes the susceptibility to small-pox just as it does to a 

 second attack of vaccina, is still more important, since it has been 

 shown that even this protection is only temporary, and that vaccina- 

 tion must be repeated from time to time, if we would prevent a return 

 of the liability to small-pox. Leaving out of consideration certain 

 foolish objections, that have been advanced against vaccination, it can- 

 not be denied that it sometimes endangers life, and in other cases 

 leaves permanent impairment of health, especially cutaneous erup- 

 tions, and other scrofulous affections. The hypothesis that scrofula 

 was transferred, by the vaccination, from one child to the other, is 

 false, as may be proved. Sometimes children become scrofulous after 

 vaccination, although the lymph have been taken from the arm of a 

 perfectly healthy child ; and sometimes children remain perfectly 

 healthy after being vaccinated with lymph from a decidedly scrofulous 

 child. The occurrence of scrofula after vaccination seems to be due 

 to the debilitating influence of the fever accompanying the vaccina, 

 and the prominence of the exanthema among these scrofulous affec- 

 tions appears to depend on the disease of the skin, artificially induced 

 at the point of vaccination. At least other febrile diseases, as well as 

 all debilitating affections, occurring in young children with a tendency 

 to scrofula, have the same influence in developing this disease that 

 vaccina has. And we know that blisters, and other irritants to the 



