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ra 1833 to describe a form of arterial disease which makes the vessel walls abnormally hard and brittle. The arteriosclerotic lesion is very varied in form. Its chief features are a thickening of the vessel walls due to cellular proliferation, the deposition of hyaline material, infiltration with various lipoids and calcification. In addition there is some degree of fibrosis, increase on occasion of elastic tissue and muscle fibres. The processes concerned in these changes are in part physiological and in part pathological. Thus in the involution of an artery such as occurs normally in the closure of the umbilical vessels and the ductus arteriosus there is a thickening of the intima due partly to cellular proliferation and partly to the deposition of hyaline material which leads to obliteration of the lumen. Again the changes which take place in arterial growth Play a part in the arteriosclerotic changes which are found associated with persistent hypertension, namely,