A dosage of 600 r to mice and 850 r to rats did not interfere with the ability of the RES to clear colloidal particles from the blood. However the 850 r x-ray dose to rats prevented recovery of normal phagocytic function after "blockade."

In mice, 600 r interfered with the ability of the RES to respond to the usual stimulating effect of zymosan.

The ability of the RES of mice which have received 600 r of x-rays to clear P³²-labelled E. coli from the blood was not significantly altered. These mice responded poorly to immunization, as demonstrated by the slow rate of clearance of the bacteria from the blood of immunized, irradiated individuals as compared with that of immunized controls. This reflected the lowered antibody production and not deficiency of phagocytic mechanism.

There was no evidence of a changed capacity of the Kupffer cells of mice which had received 600 r of x-rays to break down denatured protein enzymatically.