1)ISEASES Oi^ THE ItEAKT. — HYPERTROPHY. 271 



wholly formed by the right one. The apex-beat often becomes 

 indistinct ; in its stead We iind a basic impulse due to the contact 

 of the conus arteriosus (fig. 84, d) with the chest-wall during 

 each systole, in consequence of the enlargement of the base of 

 the heart in its antero-})Osterior diameter. 



§ 235. Hypertrophy of the heart is invariably due to over- 

 work ; it is caused by mechanical hindrances to the onward 

 flow of the blood. These increase the labour of the heart by 

 augmenting the pressure Avhich at the beginning of each systole 



Hypertrophy of right Ycntricle. Heart in situ. References as 

 in previous figure. The dotted line represents the outline 

 of the hypertrophied right ventricle. 



acts vertically against the inner surface of the ventricle, and 

 which has to be overcome by its contraction. We have already 

 seen hypertrophy of the left ventricle associated with atheroma- 

 tous degeneration of the aorta ; we shall soon become acquainted 

 with lesions of the cardiac valves as by far the commonest 

 causes of hypertrophy, and we shall find ourselves obliged to 

 refer to the subject again and ag^in in discussing other organic 

 diseases. As regards the histological details of hypertrophy of 

 the muscular substance of the heart, the hypothesis that the 



