564 HEART (DISEASES OF THE) tion. Emphysema of the lungs, and sometimes other affections which impede the free circula- tion of blood through these organs, involve an over filling of the right ventricle with blood ; and the mechanism of the hypertrophy and dilata- tion which follow is the same as when the en- largement is caused by valvular lesions. En- largement also occurs in some cases of chronic disease of the kidneys, the probable explanation being that the circulation through the capillary vessels is impeded, and hence the heart is excited to increased muscular exertion. Enlargement of the heart in different cases has its primary seat in different portions of the organ, and the enlargement of certain portions predominates. Thus valvular lesions at the aortic orifice in- duce first and especially enlargement of the left ventricle ; mitral lesions lead particularly to enlargement of the left auricle and of the right ventricle; pulmonary emphysema leads to enlargement of the right, and renal disease to enlargement of the left side of the heart. These facts are sufficiently explained by the immediate bearing of the causative conditions on the blood currents and the quantity of blood in the different cavities of the heart. It is a question whether enlargement is ever a result of the disturbances of the heart's action em- braced under the name functional disorder. Oases in which this causative relation exists are certainly extremely rare. The symptoms and morbid effects of enlargement vary much ac- cording as hypertrophy or dilatation predomi- 'nates, or as either exists without the other. The effects referable to hypertrophy are due to the increased power of the heart's action, proportionate to the increase of its muscular structure. If hypertrophy exist alone, or if it greatly predominate, this increased power is represented by an increased momentum of the blood in the arteries. Active congestion, more especially within the skull, is sometimes a con- sequence. This effect would be of much more frequent occurrence were it not that in most cases of hypertrophy there are valvular lesions which tend to diminish the quantity of blood sent into the arteries. Aortic and mitral le- sions, either obstructive or regurgitant, have this tendency, and hence they are conservative as regards the prevention of active congestion of the brain and other organs. The effects of dilatation are the opposite of those referable to hypertrophy. Dilatation involves weakness of the heart, and its ability to propel the blood through the arteries is lessened in proportion as the heart is dilated. This power of enlarge- ment is not, like hypertrophy, compensatory or conservative, when associated with valvular lesions ; on the contrary, many of the evils of organic disease of the heart are attributable to the weakness incident to it. Dilatation of the right side of the heart resulting from mitral lesions stands in immediate relation to general dropsy, and in a certain degree to the defective pulmonary circulation. Dilatation of the left ventricle resulting from aortic le- sions renders this part more liable to become distended with blood, causing paralysis of the muscular walls and sudden death. Enlarge- ment of the heart and its extent are easily de- termined by means of physical signs furnished by the touch (palpation) and percussion. By the touch it is found that the apex beat is more or less lowered and carried to the left of its normal situation. Between the apex and the base of the organ are often found im- pulses not perceptible in health. By percus- sion the boundaries of the organ are readily ascertained in the great majority of cases. The vocal resonance also, as heard with the stethoscope, enables the physician to define the limits to which the organ extends. Palpa- tion and auscultation furnish signs by which predominant hypertrophy may be differentiated from dilatation. If hypertrophy predominate, the impulses of the heart as felt by the hand are strong, and often there is a heaving move- ment extending over the region of the heart. The first sound of the heart, over the apex, is abnormally loud, long, and booming. On the other hand, if dilatation be considerable or great, weakness of the organ is denoted by feeble impulses and by diminished intensity to- gether with shortness and a valvular quantity of the first sound of the heart in the situation of the apex. With these physical signs are associated, on the one- hand, symptoms and effects denoting a morbid increase of the pow- er of the heart's action in hypertrophy, and on the other hand, in dilatation, those proceed- ing from a morbid feebleness of the organ. Hypertrophy of the heart seldom calls for treatment with a view to lessen or remove this lesion. To do this would in general not be desirable were it practicable; and it is not practicable, because the hypertrophy is in most cases a result of conditions which of necessity continue. It would not be desirable, inasmuch as the lesion protects against the evils which would otherwise flow from the causative con- ditions, and it is therefore a conservative pro- vision against these evils. It is different with dilatation ; it is desirable to prevent the pro- gress of this kind of enlargement, and to ob- viate the weakness of the heart which it induces. Measures of treatment may do con- siderable toward the accomplishment of these objects. The heart may often be strength- ened by dietetic, hygienic, and medicinal mea- sures to promote assimilation and nutrition; and in as far as the muscular structure of the heart is rendered strong and vigorous, it is less likely to yield to the distention of the blood within its cavities and become more and more dilated. There are some remedies which seem to exert a direct tonic influence upon the mus- cular structure of the heart. Digitalis is pre- eminently a remedy of this character. By the judicious use of this remedy in conjunction with hygienic treatment, the heart sometimes regains in a measure the strength which has been impaired by dilatation, the distressing
