In simple hypertrophy, the walls retain their _normal thickness_, while the shape may be changed according to the cavity affected. Passive dilatation, on the other hand, is accompanied with _thinning_ of the walls, and usually results from fatty degeneration, atrophy, or some other change in the muscular fibre. =Atrophy.= In this condition there is a uniform decrease in the size of the heart. Its cavities becomes small, and its walls thin. It usually attends diseases accompanied with great impoverishment of the blood, as in cancer, diabetes, etc., or may result from obstruction of the coronary arteries from calcification, atheroma or thrombi. Paget mentions a case where the heart of a cancerous man, fifty years old, weighed only five ounces, four drachms; and that of a diabetic woman, which weighed only five ounces, one drachm. It is usually accompanied with a general wasting of the tissues and organs of the body, and frequently will be found associated with fatty degeneration, which will now be noticed. 4. Morbid Condition of the Walls Alone. =Fatty Degeneration.= Two forms of fatty diseases of the heart have been recognized. In the first, which should be known as “_fatty growth_,” to distinguish from “_fatty degeneration_,” there is an unusual quantity of adipose matter in those parts of the heart where more or less is usually found, viz.:—Along the furrows through which the vessels run, and particularly about the base of the heart. The fatty masses may dip more or less into the substance of the walls, displacing the muscular fibres, although the latter are generally normal in color and density, even when imbedded in masses of fat. This condition may be found in persons who are otherwise thin, as well as in the obese. But the more frequent form of fatty disease, is that known as _fatty degeneration_. In this, we find upon opening the heart, that it has lost the reddish-brown color characteristic of the muscular fibre in its normal condition, and is pale, soft and flabby. The whole organ feels soft, doughy and inelastic, much like a heart beginning to decompose. If the wall of the left ventricle be partly cut through, the remainder is easily torn, and the surfaces have a granulated appearance. Upon the inner surface, beneath the endocardium, numerous small thickly set spots, or sometimes wavy lines, of a pale buff, or light yellow color, may be noticed. This appearance does not depend upon a deposit of fat among the muscular fibres, but rather upon a change in that tissue; and an examination with the microscope, will show fatty degeneration of the fibre.