EPIDEMIC AND ENDEMIC DISEASE 273 



hand, when a community is large, and especially when it enjoys 

 constant intercourse with other considerable centres of population 

 air-borne disease prevails in endemic form, mild exacerbations of 

 which are termed epidemics. Nearly every one suffers during 

 youth. The non-resistant perish, the resistant acquire immunity. 

 New births supply materials sufficient to secure the persistence of 

 the disease, and provide for the so-called epidemics; but the 

 microbes never become so abundant as when they invade a new 

 country and infect the whole population. Therefore children may 

 not be infected until several years after birth. 



453. Disease, when endemic, is far less terrible than when 

 epidemic. In the former case the sick are tended, the treatment 

 is understood, and the business of the community is not impeded. 

 In the latter, so great may be the number of adult sufferers 

 that the sick receive scant attention, and so considerable the dis- 

 location of business that famine may follow. Disease, when 

 endemic, does the work of selection much more 'cleanly' and 

 thoroughly than when epidemic. Practically every non-resistant 

 person is eliminated, but few people perish from neglect or starva- 

 tion. Epidemic disease, on the other hand, causes the death of 

 numbers of people whose powers of resistance are considerable, 

 while it spares during its intervals of absence many others whose 

 resisting powers are low. It selects in a much less discriminating 

 fashion. 1 



454. Formerly smallpox was endemic in Europe in the same 

 way as measles is to-day. At present vaccinia is endemic. The 

 disappearance of smallpox coincided with the prevalence of 

 vaccinia. A considerable portion of the community, including 

 some men distinguished in science or of great intellectual activity, 

 insist that the two events had no causal connection, and therefore 

 that vaccinia is not a preventive of smallpox. But, if they are 

 right, it is difficult to conceive what can have banished the latter. 

 It cannot have been sanitation, for smallpox is an air-borne 



1 We noted that sanitary science has absolutely no control over air-borne 

 disease. In England it is customary to close the schools during an epidemic of 

 measles, chicken-pox, mumps, or whooping-cough. It is a question whether 

 " the game is worth the candle," at any rate as a preventive measure. Speaking 

 practically, every susceptible child and innately unsusceptible children are 

 rare is sure to acquire the disease sooner or later. The danger from chicken- 

 pox and mumps is negligible. Measles and whooping-cough are more dangerous 

 to infants than to older people, but not appreciably more dangerous to school 

 children than to adults. If these diseases are inevitable, it is perhaps better that 

 they should be done with early in life, when time is less valuable and the incon- 

 venience not so great as later. 

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