1893.] Bacteriology in its General Relations. 851 
immunity. The conditions must first be worked out experi- 
mentally upon the lower animals, and it will require patient 
and extended research before they can be applied to human 
ills. The most pronounced results so far in this connection, 
are accomplished by the blood serum therapeutic methods, as 
demonstrated by Behring and Emmerich. This theory rests 
upon the conception that in an animal artificially immuned, 
a certain change has taken place in the blood serum by which 
it has become endowed with antibacterial, as well as with anti- 
toxie properties; also that the serum of an animal thus pro- 
tected possesses in itself a positive therapeutic value. Kitasato, 
two years ago, succeeded in rendering mice so refractory tow- 
ard the poison of the tetanus bacillus, that they were able to 
withstand an injection of three hundred times the ordinary fatal 
dose. Theserum of theseimmuned animals when injected into 
susceptible controls, that had been infected with virulent tetanus 
eultures was able to arrest the progress of the disease even 
after the characteristic symptoms of tetanus had been mani- 
fested throughout the body. Not only has this course been 
applied to experimental tetanus in mice, but rabbits, dogs, 
horses and sheep, all of which are susceptible to the disease, 
have been rendered refractory by these artifical methods. 
This plan of treatment has recently been used in tetanus in 
man. The curative substance was secured from the serum of 
artificially immuned rabbits and dogs, and there are already on 
record over a dozen cases of human tetanus that have been suc- 
cessfully treated by this method of inoculation. Some of the cases 
were so far advanced that paralysis had already set in, yet the 
injected material was able to neutralize the toxicity of the poi- 
son, and inhibit its further production. The application of 
this method to other diseases analogous in character promises 
favorable results, and the problem to-day in this connection, 
lies not so much in further proof of the theory, as it does in 
the ability to artificially immunize animals of adequate size to 
procure the serum in sufficient quantities to be utilized in 
actual practice. Behring has succeeded with diphtheria in 
conferring immunity upon rabbits and guinea pigs and has 
found that their serum is likewise able to check the experi- 
