There is no disharmony in the nature of old people so striking as this transference of the lime salts from the skeleton to the blood-vessels, producing as it does a dangerous softening of the former, and a hardening of the latter that interferes with their function of carrying nutrition to the organs. It is the manifestation of an extraordinary disturbance of the properties of the cells that compose the body. The atheromatous condition of the arteries is closely linked with arterial sclerosis, an affection which is very common, although not constant, in the aged. The whole question of these vascular alterations is extremely complex, and before it can be cleared up, a number of special investigations must be made. Probably diseases of the arteries of different kinds, and arising from different causes, are grouped under the terms atheroma and sclerosis. In some cases the lesions are inflammatory and are due to the poisons of microbes. An example of such an origin is the case of syphilitic sclerosis, in which the specific microbes (spirilla of Schaudinn) lead to precocious senescence. In other cases the arteries show phenomena of degeneration resulting in the formation of calcareous platelets which interfere with the circulation of the blood. Investigations which have been made in recent years have led to very interesting results concerning the origin of atheroma of the arteries. In most cases, attempts to produce such lesions of the arteries by experimental methods have not succeeded, but M. Josué[19] has been able to produce true arterial atheroma in rabbits by injecting into them adrenaline, the secretion of the supra-renal capsules. This experiment has been repeated many times and is now well known. Later on, M. Boveri[20] obtained a similar result by injecting nicotine, the poison of tobacco. It is obvious, therefore, that amongst the arterial diseases which play so great a part in senescence, some are chronic inflammations produced by microbes, whilst others are brought about by poisons introduced from without. It is easy to understand, therefore, why these diseases of the arteries are not always present in old age, although they are very common.