Abstract
The lesions produced by the Shwartzman and Arthus phenomena, as well as those produced by bacterial toxin and foreign sera in the normal rabbit, are spread by testicle extract over a larger area than would normally take place. With this spreading of the lesions there is a definite reduction in their intensity. Lesions produced by invasive strains of staphylococcus at high dilutions or non-invasive staphylococci at moderate dilutions are definitely lessened in severity or even suppressed by the spreading action of testicle extract. Virus lesions are consistently enhanced by the spreading factor regardless of the dilution.