DISEASED ACTION OF THE HEART. 657 



by all those conditions which may be characterized as stimulating or 

 strengthening, such as exercise, food, stimulants, repose, and so on ; 

 whilst depressing and weakening conditions, on the other hand, lessen 

 its force. Stimulating medicines, such as ammonia, ether, or alcoholic 

 preparations, increase the force and frequency of the heart's beats ; 

 whilst sedatives, and especially digitalis, diminish their frequency, the 

 latter drug not lessening the force. The impulse of the heart, gener- 

 ally proportional to the strength of the body, is affected by various 

 conditions ; it is least felt in the recumbent position, on the back or on 

 the right side, and most distinctly in the prone position, or when lying 

 on the left side ; in the upright posture it is moderately strong. The 

 impulse of the heart is less manifest in stout persons, but much more 

 evident in thin ones ; it is also more perceptible during a forcible ex- 

 piration, and less so during a powerful inspiration, because, in the 

 latter case, the heart is overlapped by the inflated lung, whilst in the 

 former, it approximates closely to the walls of the chest. It is also 

 increased by exciting causes, such as exercise, food, stimulants, and 

 certain emotions which produce the so-called perceptible impulses con- 

 stituting palpitation of the heart. As already mentioned, the rhythm 

 of the heart may be interfered with by causes acting through the ner- 

 vous system, in which case it may even become irregular, so that suc- 

 cessive beats of the heart take place at unequal intervals of time, or 

 certain beats may altogether intermit. 



Lastly, the force, rhythm, impulse, and likewise the sounds of the 

 heart, are variously modified by morbid conditions of that organ and 

 the adjacent parts, as by thickening or hypertrophy, thinning or 

 atrophy, of its walls, thickening and imperfect closure of, or irregular 

 growths on its valves, adhesion of the pericardium to the heart, or the 

 presence of membranous deposits or fluid between it and that organ. 

 The impulse and sounds may even be altered by affections of the lungs, 

 pleura, or thoracic walls. The morbid changes in the sounds of the 

 heart, are distinguished by terms descriptive of their character, posi- 

 tion, cause, or period of occurrence. Thus, there are murmurs blow- 

 ing or rasping, and friction-sounds ; mitral or tricuspid sounds ; aortic 

 or pulmonary; regurgitant or constrictive ; diastolic or systolic. The 

 most marked and frequent murmurs are the mitral regurgitant, from 

 imperfect closure of the mitral valve, and the aortic constrictive, from 

 narrowing of the orifice of the aorta. General enlargement of the 

 heart increases the area of local dulness on percussion of the chest, 

 due to the contrast between the solid heart and the inflated lung. 

 Fluid effused into the pericardium, also increases the dulness ; but, 

 moreover, it weakens or gives a distant character to the heart's sounds. 

 Drier and solid effusions, as of lymph, cause a peculiar pericardial 

 friction-sound, or even tremors, which m-ay be felt in the thoracic 

 parietes, dependent on a rubbing together of the surfaces of the 

 heart and its perica>rdial sac. 



42 



