. Diseases of the heart and thoracic aorta. ffer, then the left auricle, and last of all theright auricle. When the lesion is due to disease of the coronary artery,the fatty change is usually more localised, and may be limitedto small portions of the organ, the exact position depends ofcourse upon the distribution of the branch of the artery whichhappens to be affected. On microscopical examination, the affected muscular fibresare seen to contain little molecules of 9il which stain blackwith perosmic acid ; these molecules are very minute, andare, for the most part, singularly uniform in size
. Diseases of the heart and thoracic aorta. ffer, then the left auricle, and last of all theright auricle. When the lesion is due to disease of the coronary artery,the fatty change is usually more localised, and may be limitedto small portions of the organ, the exact position depends ofcourse upon the distribution of the branch of the artery whichhappens to be affected. On microscopical examination, the affected muscular fibresare seen to contain little molecules of 9il which stain blackwith perosmic acid ; these molecules are very minute, andare, for the most part, singularly uniform in size ; in somecases they coalesce and form minute globules which seldom,however, exceed the size of half a red blood corpuscle. Thefatty molecules are sometimes arranged in rows, but areusually distributed in an irregular manner throughout thewhole thickness of the fibre ; as the change progresses, thetransverse strise become indistinct and finally disappear, thewhole fibre ultimately becoming filled with little oily par-ticles. (See fig. 258.). Fig. 2^%.—Muscular fibres of the heart in a case of fatty degeneration,a, a, a, fibres in which the fatty change is just commencing; b, b, fibres in which it is far S 642 Diseases of the Heart. Muscular fibres affected Avith fatty degeneration are muchmore brittle than healthy ones, and readily break up trans-versely into short fragments. In fatty hearts it is not at all uncommon to find thecondition which has been termed brown atrophy, in whichpigment particles are deposited around, more particularlyat the ends or poles of the muscle nuclei. The connectivetissue nuclei, and the fibrous septa between the fibres aresometimes also increased ; this change is chiefly, I think,observed in hypertrophied hearts, more especially in thoseconditions, such as mitral regurgitation, in which the venousreturn from the cardiac walls is interfered with. Fat cellsare, of course, seen between the muscular fibres, in thosecases in which fatty dege
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