224 HUMAN DISEASES 



structures. The senses of hearing and touch and possibly of smell 

 become very acute in the blind, and civilized children are supplied 

 with such Jsoft food that their jaws are not stimulated to the 

 utmost possible development. Their teeth, which owe nothing to 

 the stimulus of use, and therefore attain their full size, are crowded 

 irregularly together in the small jaws, and while retaining fragments 

 of fermentable food in their interstices, are not cleansed by the 

 tough fibrous substances which form a prominent part of the diet 

 of savages. 1 They are therefore particularly exposed to decay. 

 African negroes have magnificent teeth ; their relatives in America 

 suffer much from caries ; yet only a few generations separates the 

 American black from a savage ancestry. 



369. It follows that though man has not now so strenuous 

 nor so active a struggle for mere existence as formerly, though 

 exceptional strength, activity, endurance, beauty, or cleverness do 

 not at the present day imply as a rule more than an average 

 number of offspring ; though men perish so very rarely and in such 

 a haphazard manner from wild beasts and enemies and from priva- 

 tion that there is no real selection, though modern, weapons of war 

 do not discriminate between the fit and the unfit in battle, yet since 

 man's ancient characters are firmly established and since con- 

 spicuous defect still acts, on the average, as a bar to offspring, he 

 has undergone little retrogression. Of progression on lines of 

 ancient characters there is no valid evidence. 



370. Nevertheless, since men still perish in great numbers 

 before contributing their full quota of offspring to the race, some 

 sort of selection is occurring. Our facilities for ascertaining its precise 

 nature are particularly good. Indeed, this is the only instance in 

 nature in which the operations of Natural Selection may be 

 observed, not merely guessed at. In every civilized country tables 

 of mortality are compiled from which we may learn exactly the 

 causes which eliminate the inhabitants of civilized states, the number 

 of deaths due to each cause, and the ages of those who perish. In 

 the vast majority of instances civilized men die of disease? Disease 



1 J. Sims Wallace, Decay in Teeth (London, Churchill). 



* In England and Wales 520,031 people died during the year 1905. Of these 

 19,437 perished of violence, mainly the result of accident in flood or field or in 

 mines. Among the violent deaths, however, were 133 from homicide, 17 from 

 execution, and 3 from battle; 21 persons died from starvation, 2638 committed 

 suicide, but probably many of these suffered from physical or mental diseases ; 

 813 are said to have died of plague. The remaining half million perished almost 

 exclusively from disease, including from tuberculosis 55,759, pneumonia 44,367, 

 bronchitis 38,9 15, cancer 30,221, diarrhoea 20,534, measles 11,076, whooping-cough 

 8709, influenza 6953, diphtheria 5459, scarlet fever 3834, cirrhosis of liver 4008, 



