292 C. G. CAMPBELL 



the pre-historic American horse to a germ infection analagous to rinder-pest, 

 carried by a fly. This inference has received a certain support from the 

 subsequent discovery of a fossil tsetse fly. A similar occurrence among 

 cattle is to be observed in Africa today. The most plausible explanation 

 that has been offered for the decline of the great Maya race and its civiliza- 

 tion is in a lethal endemic or epidemic germ infection. A similar cause has 

 been inferred for the disappearance of racial groups in other instances. 

 The Black Death of the Middle Ages is computed to have destroyed 60 

 per cent of the population of Europe. In 1919 a world-wide epidemic of 

 influenza, which medical science could do little to arrest or to combat, 

 gave us a mild idea of the human toll that a germ infection can take. It 

 is not difficult to envisage much more serious results in the future in the 

 event of any marked lowering of the general average of racial vitality and 

 resistance. 



Biological nature, in what some might regard as its crude and cruel way, 

 sacrifices many individuals in the invasion of infections. But a species 

 emerges with an augmented resistance in the surviving remainder, which 

 tends to become in time a thoroughly protective immunity. A race is mani- 

 festly stronger in its resistance that has acquired a measure of immunity 

 through long exposure to infections than one that has escaped exposure or 

 been protected from them. For example there is a large measure of resist- 

 ance and immunity in European races from long exposure to tuberculosis, 

 the germs of which all individuals breathe in daily. This immunity would 

 be much greater if racial strains which were susceptible to tuberculosis did 

 not interbreed, or made a determined effort toward outbreeding. But while 

 the incidence of tuberculosis in European races might still seem to us all too 

 great, it might be cited that in a company of 30 or 40 Esquimaux, which was 

 brought on one occasion to an American exhibition, something like half of 

 them contracted tuberculosis within six weeks, whereupon the rest were 

 promptly returned to their northern habitat. 



It has recently been discovered that the remnant of the Maya race that 

 survives is highly immune to syphilis. Those who contract it recover spon- 

 taneously with no serious effects. But many, if not most, are wholly im- 

 mune to it, and do not contract it on exposure. The reasons for this immu- 

 nity have yet to be demonstrated, but the most likely inference would be that 

 it arose from syphilis being endemic in this race for many generations, until 

 a completely protective immunity was established. If this is so, it would 

 go to confirm the supposition that syphilis was originally indigenous to 

 America, and was only introduced into Europe after the discovery of Amer- 

 ica. This does not necessarily indicate however that syphilis was the par- 



