850 The American Naturalist. [October, 
successful method of action in repressing it than any we have 
heretofore possessed. 
Prophylaxis, or preventive treatment, may be carried on in 
two ways. We may prevent disease, either by destroying the 
cause of the infection, or by rendering our bodies refractory to 
the attack of the disease germ. The first is accomplished 
by disinfection, the latter by preventive inoculation. What 
Jenner did with small-pox is an entirely empirical man- 
ner, modern bacteriology has effected in the light of estab- 
lished principle. The brilliant researches of Pasteur and his 
pupils along these lines, not only in the case of human infec- 
tion as in hydrophobia, the mortality of which at the Pasteur 
Institute at Paris has now fallen to less than one-half of one 
per cent., but also certain animal diseases like splenic fever in 
sheep and cattle, erysipelas in swine and cholera in fowls, are 
practical testimonials of the advance that modern bacteriology 
has to offer in the direction of prophylactic treatment. The 
Berlin school, while it has not as yet succeeded in applying 
its methods in so widespread and practical a way, has placed 
the question of acquired immunity upon a firmer scientific 
basis. The discoveries of Friinkel, Brieger, Kitasato, Behring, 
and Ehrlich are all of supreme importance from an experi- 
mental standpoint. These observers have been able to 
immunize various animals by artificial means against such 
diseases as tetanus, diphtheria, pneumonia and erysipelas of 
swine. Not only have they endowed the animal body with 
such properties that it can successfully antagonize either the 
germ or its toxic product, but in some cases, have actually 
restored the animal to its normal healthy condition after the 
disease had been established.’ 
How far these results can be utilized in combating disease 
in the human system is not yet definitely known. In the con- 
sideration of the probable value of these results to therapeutics, 
we need to be conservative in our conclusions, for the condi- 
tions are widely different between an experimental disease in 
animals and its natural course in man. From the present 
outlook, it seems that any permanent advance along this line 
will be based upon successful efforts in securing artificial 
