Subsequent to the publication of an article by Hans Zinsser, George W. McCoy and C. W. Chapin1 on The Protective Influence of Leukocytic Substances on Experimental Plague, one of us conceived the idea that if leukocytic substances could be obtained in sufficient quantities to be not only therapeutically practical, but commercially possible, a decided step forward would be made in the biological treatment of infectious diseases.
Prior to the publication of the above mentioned article, Hiss and Zinsser2 demonstrated in an experimental way that leukocytic extracts could be prepared by injecting into the pleural cavities of rabbits 10 c.c. of a meat extract broth containing 3 per cent. starch and 5 per cent. aleuronat. At the end of twenty-four hours a copious, and very cellular exudate will have accumulated in the pleural cavities. This is obtained by killing the rabbits, and removing the exudate which is immediately