184 THE TREND OF THE RACE 
whooping cough, measles, scarlet fever and diphtheria are very 
prevalent among all classes. The mortality of the first three is 
much greater among the children of the poor, whereas diphtheria 
when allowed to run its natural course has a high mortality among 
rich and poor alike. With measles and whooping cough mortality 
is largely dependent upon general health, whereas with diphtheria 
this is not nearly so obvious. 
Some epidemic diseases are doubtless selective in their nature, 
eliminating to a greater degree those with weakened constitutions, 
whereas others apparently possess little selective value so far as 
can be observed. Some diseases, therefore, may be racial bles- 
sings in disguise, whereas others may have simply a depressing 
influence on the race as a whole. There is evidence to show that 
in the white race there are different degrees of susceptibility to 
several diseases correlated with differences in the degree of pig- 
mentation. Baxter, in his study of large numbers of soldiers of 
the Civil War, concluded that those with a light complexion were 
more liable to disease and suffered more from their injuries than 
those with a dark complexion. The proportions of recruits re- 
jected for military service were, among the blonds, 385.2 per 
thousand, and among the dark complexioned, 325 per thousand. 
Eye troubles in the two classes were in the proportion of blonds 
22 and dark 18. In Scotland, according to Tocher, the incidence 
of insanity is greater among the people of light colored eyes. 
McDonald has studied the relation between pigmentation and 
disease in a large number of children in the hospitals at Glasgow. 
He finds that in regard to diphtheria, whooping cough, scarlet 
fever and measles, ‘‘the dark-haired, dark-eyed child has consid- 
erably more recuperative power than the fair-haired, light-eyed 
child. The medium-haired medium-eyed child occupies an inter- 
mediate position as regards recuperative power.” ‘The closer 
the type approximates the fair, the less recuperative power it has, 
and the less resistance it offers to the diseases.” 
These results are quite parallel to what has often been observed 
among animals. Darwin states on the authority of Professor 
Wyman that dark pigmented swine in Virginia eat with impunity 
