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 lias 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. 
