When a foreign protein is injected into the blood stream, it has been observed that the number of leukocytes is at first usually diminished, later markedly increased and that finally there is a gradual decrease, the number of leukocytes falling to approximately the original level. It also has been observed that during the height of digestion and absorption in the small intestine, the leukocytes are increased in number.
In connection with a study on the effect of ingestion of yeast in certain pathologic conditions, we were interested in a consideration of the mechanism of its action. In cases of infection, it is generally assumed that an increase in the number of leukocytes indicates a satisfactory response on the part of the organism in defending itself against the invading bacteria. There are, however, numerous investigators who do not believe that an increase in the leukocyte count necessarily accompanies such a defensive