144 
HOUSEHOLD BACTERIOLOGY 
the daily newspaper, for which the discovery overnight 
of a new “serum” seems to furnish an item of per¬ 
petual interest. 
The reasons for this failure are in part evident to 
experts in this field, in part arc still very obscure, and 
are too technical to be entered upon here. But the 
eager and toilsome search goes on wifji such inspira¬ 
tion as is ever his who deals with these urgent prob¬ 
lems of life and death, and at any moment the key to 
the riddle may lie in our hands. 
It would be interesting, did the scope of this article 
permit, to look at the means by which the body pro¬ 
tects itself against infection, not by neutralization of 
poisons, but by the actual destruction of the poison 
producers—the bacteria themselves. Suffice it to say 
that here also, in this bacteria-destroying phase of 
immunity —germicidal immunity, it is called—the body 
does not command new forces or mechanisms, but 
makes use of those which are maintained for its daily 
service, but which in the emergency it wields to new 
ends and with exalted energy. 
OTHER METHODS OF PROTECTION. 
When it was found that it was not possible at once 
to secure antitoxic sera for other infectious diseases 
in the way which had been so successful with diph¬ 
theria, the attempt was made to obtain protection in 
some other way. The leading idea in these researches 
was to find a method of adapting man to pathogenic 
germs without exposing him in the process to the 
