108 ORGANIC DEPENDENCE AND DISEASE 



Many writers on the causes of extinction among the ver- 

 tebrate races of the past have predicated much of germ 

 infestations. Perhaps no one has more effectively summa- 

 rized these causes of extinction than Henry Fairfield Os- 

 born. 1 Any student who seeks suggestive evidence of an 

 intensifying cause of race extinction which is wholly collat- 

 eral to the imperious control of decline in racial vitality, 

 will be impressed by the facts which have been set out in 

 detail by Professor Osborn. From them, however, we can 

 glean no conclusive deduction that any such attacks from 

 external agencies, however devastating the records show 

 them to be at the present time, trypanosomiasis, rinder- 

 pest, tick fevers, sulla, uncinariasis and other such patho- 

 logic expressions which sweep away their victims in epi- 

 demics, have ever reached the climax of actual race 

 extinction. Notwithstanding the raids by these agents and 

 the check which they put upon reproduction, still the subject 

 races seem to possess sufficient adaptability and surviving 

 competence to outlive them. It is easy to understand that 

 such might not be the case with a declining stock whose 

 racial vitality is already departing and whose impending 

 extinction might well be accelerated by such invasions. In 

 phases like this it may well be conceded that, as an acces- 

 sory cause, germ infection has been climacteric. 



We shall have, sometime, to estimate the differential 

 effects of such epidemic attacks of protoplastic disease ac- 

 cording to, or in terms of, the vital phase of the race at- 

 tacked ; for a race at the summit of its vitality can better 

 resist and fully survive such infestation than in its declin- 

 ing stages. And it goes without further statement that the 

 growing and aspiring race which is reaching forward to its 

 climax would sturdily resist such invasions. Finally, we 

 may add that the discovery in the Tertiary rocks, of species 

 of the tsetse fly whose present-day descendants are carriers 



i American Naturalist, Nov. and Dec., 1906. Lull, Lucas, Williston and 

 Moodie have also, among others, written interestingly on this theme. 



