In presenting the results of his very suggestive studies on the agglutination of bacteria in vivo, Dr. Bull (1916) makes the following statement: From table 1 it is seen that bouillon cultures of Bacillus avisepticus are highly toxic for rabbits, 0.5 cc. of culture per kilo causing acute death. The intoxication is largely due to a toxin, since 1 cc. per kilo of body weight of a bacteria-free filtrate from a twenty-four hour culture causes acute death. and again:These results especially emphasize the significance of agglutinins and opsonins in the mechanism of natural resistance to infection, since Bacillus avisepticus produces a powerful toxin and is still incapable of causing a septicemia of any consequence in the presence of these antibodies.