CHAP. xvm. VACCINATION A DELUSION. 290 



deaths in the districts. The result shown is very re- 

 markable. In the most thinly populated district no 

 small-pox death occurred in any one of the twenty-four 

 years; in the most densely peopled districts small-pox 

 deaths occurred in every one of the twenty-four years. 

 And the frequency of the occurrence of small-pox in all 

 the intervening groups of districts followed exactly the 

 density of the population. Taking two groups with 

 nearly the same population, the fourth group of 107 dis- 

 tricts, with a total population of 1,840,581, had small- 

 pox deaths in only five or six out of the twenty-four years 

 in any of them; while the thirteenth group of thirteen 

 districts, with a population of 1,908,838, had small-pox 

 deaths in twenty-three out of the twenty-four years. 

 But the first group had a density of 160 to the square 

 mile, and the last had 8350 to the square mile. The 

 Commissioners dwell upon the alleged fact that neither 

 water-supply, nor drainage, nor contaminated food 

 produces small-pox, and urge that what is commonly 

 understood by sanitation has little effect upon it (par. 

 153). But what may be termed the fundamental prin- 

 ciple of sanitation is the avoidance of overcrowding; and 

 this is shown, by an overwhelming body of evidence, in- 

 variably to influence small-pox mortality quite irrespect- 

 ive of vaccination. 1 Yet the remarkable contribution 



1 It is not alleged that overcrowding, per se, is the direct cause of 

 small-pox, or of any other zymotic disease. It is, perhaps rather a 

 condition than a cause ; but under our present social economy it is so 

 universally associated with various causes of disease impure air, bad 

 drainage, bad water supply, unhealthy situations, unwholesome 

 food, overwork, and filth of every description in houses, clothing, and 

 persons that it affords the most general and convenient indication of 

 an unhealthy as opposed to a healthy mode of life ; and, while 



