MICEOBES— INFECTION— IMMUNITY 465 



strains of the bacilli, as it is found from experience these 

 are frequently of different degrees of virulence. 



Finally, the injection of serum, for the prevention of 

 tetanus among horses which have to be operated upon in 

 notorious tetanus localities, is a measure which may be 

 adopted, the serum in this case being a pure anti-toxin. 



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