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The presence and distribution of two groups of enzymes has been determined histochemically on sections of the schistosome-bearing snail Australorbis glabratus. By the use of specific inhibitors, attempts have been made to characterize further the enzymes occurring in the various organs and tissues.

As a result of this study it has been found that alkaline and acid phosphatase are widely distributed but have identical localizations only in the kidney and albumen gland. Both enzymes react typically to the action of the usual inhibitors.

Among the non-specific esterases. an enzyme corresponding to the mammalian A-type esterase (aromesterase) is present in the brain; while a B-type esterase (aliesterase) is located in the digestive gland, intestine, and on the glandular region of the foot surface.

A “true” lipase (an esterase acting on an undissolved substrate) is found principally in the albumen gland, with an indication of its presence in the digestive gland and in portions of the digestive tract.

An enzyme with the properties of an acetylcholinesterase occurs in the radula sac, oesophagus, preputium, junction of carrefour and oviduct, and amoebocytes. A positive reaction for cholinesterase is also obtained with frozen sections of brain but, although this enzyme has been shown biochemically to hydrolyse acetylcholine and is inhibited by low concentrations of eserine. it is remarkably resistant to the action of organophosphorous compounds, and its true nature cannot he stated with certainty.