1897 THE MICROSCOPE. 37 
hoid fever, tuberculosis, glanders and a number of other 
diseases, 
This led to another discovery, more important and far- 
reaching. Fodor showed that the blood serum of animals 
made immune to a particular disease by injecting the 
animal with the poison which the germ formed, had the 
effect of destroying the germ of the disease, This ex- 
cited renewed interest in the study of the blood and with- 
in a few years it was demonstrated in the Washington 
laboratories, by Behring, by Roux and others, that this 
serum from previously immunized animals, not only had 
the property of conferring immunity upon other animals, 
but also of checking the disease after it had started, and 
we know that many thousands of lives have been saved 
by the anti-toxine serums. 
How SERUM Is SECURED.—To prepare these solutions, 
toxins, such as have already been described, are injected 
into different animals, preferably horses, and at the end 
of six to twelve weeks the bkood of these animals is found 
to yield a serum containing substances possessing the 
immunizing and curative properties which we call anti- 
toxins. The active principle of this serum is compara- 
tively small in quantity, but its influence is enormous. 
Recent investigations have shown that these anti-toxic 
serums can be used for protection against not only 
tetanus and diphtheria but also for typhoid fever, cholera, 
anthrax, the plague and others. These serums can be 
used also by farmers in cases of cholera in hogs and of 
tuberculosis in cattle and to check these diseases in small 
animals. 
In the case of the venom of serpents, it is found that 
repeated injections will make the serum of an animal 
anti-toxic and curative against other venoms. The anti- 
toxic serum produced by the cobra venom will protect 
against the bite of the rattle-snake. 
When milk and cream are first collected they are al- 
