blood-pressure is relatively high, reaching its maximum about 36; the aorta and other large arteries increase in diameter from the stress of the blood-pressure on their elastic walls, particularly between 35 and 45, and the heart increases in size year after year at a nearly uniform rate. We have in these facts anatomical evidence of the great functional vigour and activity of the circulation in manhood. At 45, which is practically the commencement of the period with which we are concerned, remarkable changes occur. Whilst the arteries continue to increase in circumference (somewhat more slowly than before), the blood-pressure falls and the heart begins—almost suddenly—to diminish in size; and these three features characterise the circulation for the next 20 years, that is, until the age of 65. How is this fall in the size of the heart to be accounted for? Partly by the widening of the arterial trunks and the consequent fall of pressure. But not by these only; for although the arteries had been widening even more rapidly between 20 and 45, the pressure was actually at its maximum then and the heart large, and we shall presently find other facts opposed to this view. The peripheral resistance in the systemic arteries must fall from some other cause or causes in middle age than the loss of elasticity of the arterial walls, and these causes are probably reduction of mechanical stress, due to comparative bodily relaxation, loss of vaso-motor tone in the splanchnic area, and the chronic diseases of which the subjects have died whose hearts and vessels are measured post mortem. During this phase of life also, the blood becomes more venous in quality and its hæmoglobin value is lowered.

At 65, other changes which occur in the heart and arteries are not less striking than those which I have just described. The decline of circulatory energy, and the effects of time itself on the protoplasm of the cells of the body, have so lowered the metabolic and functional energy of the tissues and organs and the activity of the blood-supply, that a considerable proportion of the capillary network becomes obsolete. The peripheral resistance is thus increased, and the blood-pressure rises; therefore the heart once more increases so much in size that at the end of the 10 years (age 75) it is found as large as it was at 45, and at the same time the hæmoglobin value of the blood again proves to be higher. During this period, also, the arteries continue to grow wider and thicker and longer—another proof that the size of the heart is not determined solely by their calibre. Regarded as a whole, the process of senescence of the cardio-vascular system presents to us a beautiful instance of anatomical readjustment and compensation—the counterpart, in a way, of the growth of the circulation in energy and activity during the period of full manhood. The arterial walls, which have been stretched in their diameter and in their length by exhaustion of their elasticity under the stress of cardiac systole, are strengthened afresh by the development of stays formed of fibroid and muscular tissues in the intima and media; and the heart responds to the altered mechanical condition ahead of it in the arteries, and to the increased peripheral resistance caused by the obsolescence of many capillaries, by growing afresh.

This account relates to the size of the arteries after 40; now let us inquire what is the condition of their structural elements. The changes described do not necessarily involve disease of the tissue elements, unless we were to call every senile change morbid. My friends Dr. Bosanquet and Dr. Mullings have given me an account of the state of the heart and aorta in the bodies of 25 men, aged 40 and upwards, examined in the post-mortem room of Charing Cross Hospital, who had died from accident or suicide. The average age was 53½ years, and the aorta presented some degree of atheroma in half the cases. When we consider how very slight a change in the arch of the aorta is habitually described as "atheroma," and that in a few of the cases the valves were diseased and the heart enlarged, we are justified in concluding that in the majority of persons of 53 the arteries are still sound. This result is in accord with that obtained by the late Professor Humphry, who devoted his attention so long and so successfully to the investigation of old age. He states that in the great majority of cases the arterial system appears to present a healthy condition in those who attain to great age.[2] Even among the majority of centenarians the evidences of arterial degeneration were not manifest.[3] And we know that we occasionally meet with people of 80 and upwards whose pulses are unexceptionable, beyond presenting a trace of thickening and enlargement.

For my present purpose, therefore, we may conclude that as age advances, the arteries naturally become wider, longer and thicker, and altogether larger than in early life; and that we must not speak of "vascular degeneration" in an evil sense as often as we find these conditions present. As for the heart, we know that it may remain structurally sound, and is more often regular than irregular, to the most advanced years of life. Conversely, these facts suggest that actual diseases of the arteries and heart, that is, other than the changes which are found in all persons after 45, are not properly senile in their nature. As Professor Humphry said, they are no part of, but are rather to be regarded as deviations from, or morbid departures from, the natural phenomena.[4] They must be the effects of pathological processes due to a variety of pathogenetic influences which assail the circulation. Now we are in a position to study these.

After the age of 40, many of the influences that threaten the heart and arteries with disorder and disease are peculiar to this period of life—that is, different and distinct from the causes of cardiac and vascular affections in childhood, adolescence and manhood; others of them have been encountered already, with or without permanent damage as the result. I will now examine them in detail, and at the same time refer to certain provisions with which the heart and arteries are endowed for resisting them and recovering naturally from their effects, as well as to the circumstances which render these provisions abortive or insufficient, and thus predispose to disease or indirectly determine its occurrence.

1. Physical stress is still a definite cause of cardiac and vascular damage during the second half of life, in the forms both of sudden violent exertion and of ordinary laborious occupations. I have met with instances of acute and serious strain at all ages over 40, up to and even after 70. I am aware that I must speak on this part of my subject—the evil effects of muscular exercise—with great caution in the presence of you, Sir, our President, who have long been recognised as one of the principal patrons in our profession of athletic sports, and so highly distinguished yourself in them at Oxford and in the inter-University contests. I assume that you are unwilling to admit that muscular exercise is dangerous to health. But I feel sure that you will agree with me that when the man of 65 rushes from his breakfast-table to catch his train, or the lady of 70 hurries up a hill in Wales to be