We have in tobacco a single distinct influence at work; one that is universally acknowledged to affect the heart and vessels, and the physiological action of which is understood; one, further, that can be removed (perhaps not without some difficulty, for I have had a patient plead for his pipe with tears in his eyes), and certainly that can always be resumed with remarkable readiness--in a word, a most favourable subject of observation by experiment. It is well, too, to begin the study of tobacco heart in young men, whose circulation is still structurally sound, and thereafter to follow up the subject in middle-aged and old persons. Adopting this line of inquiry, I have found that the uncomplicated effects of tobacco on young healthy hearts, as they present themselves clinically, are: palpitation in every instance; a sense of irregular action,[6] post-sternal oppression and pain in half the cases; and in one out of every eight sufferers either angina or uncomfortable sensations in the left arm. Faintness or actual faints occurred in one-third, and giddiness and a feeling of impending death in a smaller proportion. Turning to the physical signs, the heart proves to be of ordinary size in 50 per cent. of the patients; in a few it is very slightly enlarged; the præcordial impulse is often very weak, but occasionally increased in force and frequency, and almost as often irregular as not; the pulse tension, with insignificant exceptions, I have always found low. Very interesting, in the light of what I shall tell you later on, is the fact that of 20 of these patients complaining of the heart not one presented a cardiac murmur beyond a weak mitral systolic bruit, varying with posture or cubitus. This is in accordance with the teachings of pharmacology --that tobacco acts on the terminal branches of the vagus. [6] A medical friend who has suffered from tobacco heart assures me that at one period he could distinguish the contractions of the auricles and ventricles.