CHAP. XVIII. 



VACCINATION A DELUSION. 



249 



in the same proportion as small-pox, and they argue: 

 " If improved sanitary conditions were the cause of 

 small-pox becoming less, we should expect to see that 

 they had exercised a similar influence over almost all 

 other diseases. Why should they not produce the same 

 effect in the case of measles, scarlet fever, whooping- 

 cough, and indeed any disease spread by contagion or 

 infection and from which recovery was possible? " This 

 seems a most extraordinary position to be taken in view 

 of the well-known disappearance of various diseases at 

 different epochs. Why did leprosy almost disappear 

 from England at so early a period and plague later on? 

 Surely to some improved conditions of health. The 

 Commissioners do not, and we may presume cannot, tell 

 us why measles, of all the zymotic diseases, has rather 

 increased than diminished during the whole of this cen- 

 tury. Many students of epidemics hold that certain 

 diseases are liable to replace each other, as suggested by 

 Dr. Watt of Glasgow, in the case of measles and small- 

 pox. Dr. Fair, the great medical statistician, adopted 

 this view. In his Annual Report to the Registrar-Gen- 

 eral in 1872 (p. 224), he says: " The zymotic diseases 

 replace each other; and when one is rooted out it is apt 

 to be replaced by others which ravage the human race 

 indifferently whenever the conditions of healthy life are 

 wanting. They have this property in common with 

 weeds and other forms of life : as one species recedes an- 

 other advances." This last remark is very suggestive in 

 view of the modern germ-theory of these diseases. This 

 substitution theory is adopted by Dr. Creighton, who in 

 his " History of Epidemics in England " suggests that 

 plague was replaced by typhus fever and small-pox ; and, 



