Eosinophils were separated from other types of cells in horse blood or rat peritoneal fluid by centrifugation in concentrated albumin solutions. Eosinophils did not appear to be damaged by this separation procedure.

A technique was also devised for isolation of cytoplasmic granules from eosinophils, thus allowing studies on enzyme content of the granules.

Granules from both horse and rat eosinophils contained a number of hydrolytic enzymes, similar in variety and in concentration to those previously found in granules of rabbit polymorphonuclear leucocytes. Eosinophil granules differed from those of the rabbit granulocyte in their high content of peroxidase and the absence of lysozyme and phagocytin. On disruption of eosinophil granules by repeated freezing and thawing in saline, cathepsin, ribonuclease, arylsulfatase and beta glucuronidase were released into solution, but phosphatases were partially and peroxidase completely bound to the insoluble granule residue. Peroxidase could be extracted from the granule residue with weak acid.

Eosinophil granules thus are lysosome-like structures.

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