314 THE EVOLUTION OF LIFE 

to diminish, as far as possible, its spread to other 
members of the community. In both these direc- 
tions the work of bacteriologists has been proving of 
incalculable value. Their study of toxins, antitoxins, 
opsonins, and serum-therapy generally is gradually 
leading to brilliant results both in the prevention and 
in the cure of disease. I, however, am naturally not 
so sanguine as many others, who still pin their faith 
to ultra-contagionist doctrines, that these diseases can 
be effectively stamped out by the mere prevention of 
contagion. Believing, as we all must, in their de 
novo origin in the past, I have always failed to see 
why they may not also be engendered in the 
present, and have been impressed by the weight 
of evidence tending to show that several of them, at 
least, do so arise from time to time. Modern 
researches are now justifying this view and lending 
support, as I urged five and thirty years ago, to the 
necessity for the most diligent search into the con- 
ditions of origin of all these affections. And the 
more contagious the disease, the more important 
does the quest become. 
