Contagious {^Zymotic) Diseases. ri 



taken from an animal normally susceptible but which has been 

 rendered artificially immune, and long enough after the induced 

 immunity to avoid all risk of left-over microbes, cannot fairly be 

 called immunization, seeing that it only lasts so long as these 

 antibodies remain in the system of the animal injected. It does 

 not rouse the cells of this animal to themselves produce the 

 required antibodies and to continue such production for a length 

 of time. It is comparable rather to a dose of chloral or other 

 antispasmodic in tetanus, which will suppress the spasms so long 

 as the chloral remains in the system, but has its action limited 

 by the amount of the dose and the period up to its elimination. 

 This partakes of the nature of therapeutic medication rather 

 than immunization. 



For immunization the following conditions may be laid down 

 as most uniformly applicable : 



1. The active pathogenic products of the invading micro- 

 organism must be employed. 



2. A nonlethal dose must be employed or a succession of such 

 doses. 



3. These must be used on an appropriate subject. The 

 injected animal must not be temporarily insusceptible like the 

 meat fed rat to anthrax, nor morbidly susceptible to the 

 same disease like the ox charged with lactic acid. 



4. The immunizing product is best injected into the con- 

 nective tissue. In intravenous injection the toxin may kill 

 at once by undue potency, or may be eliminated so rapidly 

 that it has no tangible or enduring effect. 



5. In case of very deadly toxins (Rinderpest) the danger 

 may be lessened or obviated by mixing the antitoxins with the 

 toxins before injection, or by injecting first the antitoxins and 

 later the toxins. 



For serum therapy the following conditions are important : 



1 . Use a suitable animal for producing the antitoxins, and 

 raise its resistance to the specific infection by successsive 

 nonlethal injections of the products of the microbes of the 

 disease in hand. 



2. Use the resistant serum of the highly immunized animal in 

 appropriate doses for the animal to be treated. 



