This report describes additional studies of the lyo and desmo components of esterase, alkaline phosphatase, acid phosphatase, leucine aminopeptidase, and ß-glucuronidase. The techniques used have already been reported (7). Enzyme diffusion occurs to different degrees in different fixatives, and varies somewhat with each enzyme. Loss of enzymatic activity during fixation occurs as a result of both inactivation due to the chemical reaction of the fixative with the enzymic protein, and diffusion of the lyo component into the fixative. The amount of diffusion into formalin can be reduced by the addition of salts, sucrose, or methocel. The pH of the aqueous medium significantly influences the removal of the lyo fraction from the tissue section. A striking similarity can be noted in the proportions of each fraction of enzyme present in the kidney of the rat, dog, and man. The procedure of fixation and paraffin embedding of tissue blocks does not wholly prevent the diffusion of the lyo component from the tissue sections when they are subsequently immersed in the aqueous incubation medium.

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