RELATIONS OF SMALLPOX TO COWPOX 505 



While vaccination is undoubtedly efficacious in protecting 

 against smallpox, Jenner was wrong in supposing that a vaccina- 

 tion in infancy afforded protection for more than a certain 

 number of years thereafter. It has been noted in smallpox 

 epidemics which have occurred since the introduction of vaccina- 

 tion, that whereas young unprotected subjects readily contract 

 the disease, those vaccinated as infants escape more or less till 

 after the thirteenth to the fifteenth years. It has become, 

 therefore, more and more evident that revaccination is necessary 

 if immunity is to continue; and where this is done in any 

 population, smallpox becomes a rare disease, as has happened in 

 the German army, where the mortality is practically nil. The 

 whole question of the efficacy of vaccination was investigated in 

 this country in 1896 by a Royal Commission, whose general 

 conclusions were as follows. Vaccination diminishes the liability 

 to attack by smallpox, and when the latter does occur, the 

 disease is milder and less fatal. Protection against attack is 

 greatest during nine or ten years after vaccination. It is still 

 efficacious for a further period of five years, and possibly never 

 wholly ceases. The power of vaccination to modify an attack 

 outlasts its power wholly to ward it off. Revaccination restores 

 protection, but this operation must be from time to time repeated. 

 Vaccination is beneficial according to the thoroughness with 

 which it is performed. 



The Relationship of Smallpox (Variola) to Cowpox 

 (Vaccinia). This is the question regarding which, since the 

 introduction of vaccination, the greatest controversy has taken 

 place ; a subsidiary point has been the inter-relationships within 

 the group of animal diseases which includes cowpox, horsepox, 

 sheep-pox, and cattle-plague.. With reference to smallpox and 

 cowpox the problem has been, Are they identical or not ? There 

 is no doubt that cowpox can be communicated to man, in whom 

 it produces the eruption limited to the point of inoculation, and 

 the slight general symptoms which vaccination with calf lymph 

 has made familiar. Apparently against the view that cowpox is 

 a modified smallpox are the facts that it never reproduces in 

 man a general eruption, and that the local eruption is only 

 infectious when matter from it is introduced into an abrasion. 

 The loss of infectiveness by transmission through the body of a 

 relatively insusceptible animal is a condition of which we have 

 already seen many instances in other diseases, and the uniformity 

 of the type of the affection resulting from vaccination with calf 

 lymph finds a parallel in such a disease as hydrophobia, where, 

 after passage through a series of monkeys, a virus of attenuated 



