MATERIALS FOR STUDY 261 



power of resisting it and nothing more. The race should not gain 

 in beauty or muscular strength or size or anything of the sort. 1 

 Of course, it is possible that this or that character may in the 

 future be found to be correlated to susceptibility to, or to power of 

 resisting this or that disease, but, to the best of my knowledge, 

 nothing of the kind has yet been discovered. 2 



433. Very plainly, disease furnishes ideal material for investi- 

 gation of that most important problem of heredity, the causation 

 of variations. The acquirements made under the influence of 

 injury (e.g. in such chronic maladies as tuberculosis), or of use 

 (e.g. in such acute complaints as measles), are very striking and 

 peculiar, and in the case of many diseases and many races have 

 been made by every generation for unnumbered generations. The 

 germ-cells are often literally bathed in toxins, it may be for pro- 

 longed periods, as in syphilis and malaria. Their nutrition is 

 interfered with for even longer periods in such complaints as 

 tuberculosis and leprosy. Our opportunities for observation are 

 particularly good, for every one of us has had personal experience 

 of illness, and is acquainted with numerous cases of it. Any 

 amount of precise statistical evidence, furnished by Departments 

 of Public Health, concerning the different effects of disease on 

 different races, is available. Every instance of the birth of a child 

 to a parent who is or has been diseased constitutes an experiment 

 which is as stringent as any that can be consciously devised, but 

 which possesses in addition the advantage that it is made under 

 conditions that are normal to the species. Like many other 

 experiments, this experiment has the disadvantage that the effect 

 produced on the offspring, if any,'*may be so small as not to be 

 observable, or it may be so confused with spontaneous variations 

 as not to be detectable ; but in the case of every disease we are 

 able to compare many races which have suffered much and long 



1 It seems hardly necessary to insist on this, but various critics have thought 

 it necessary to declare that there is no evidence that much experience of disease 

 produces the ' finest race.' 



2 The dark colour of negroes has been thought to be correlated to their high 

 powers of resisting malaria. But many black races, for example some Polynesians, 

 are highly susceptible, and some white races are relatively resistant. Thus malaria, 

 which destroyed an invading British army as a fighting force, left the inhabi- 

 tants of the island of Walcheren able to pursue their ordinary avocations. 

 Biometric attempts have been made to discover correlations between physical 

 and mental traits and disease by comparing individuals of the same race, but if we 

 compare individuals of different races, in whom contrasts in resisting power, colour, 

 and the like are so much more marked as to be easily observable, we find no 

 such correlations. 



