Abstract
The sites of action in the central nervous system of the rat of thiamine diphosphatase, an enzyme liberating phosphate from Vitamin B1, is described and illustrated. The optic tectum of the domestic fowl has also been examined. Some histological and cytochemical properties of the enzyme in these two species is compared. The activity of this enzyme may be involved in the pathological disturbances and tissue damage occurring in thiamine deficiency.