This condition is of exceedingly frequent occurrence in the heart,, especially in its minor degrees. Any disease which causes a serious deterioration of the blood may produce it, and it is seen in its most pronounced form in the various kinds of anaemia, in leukaemia, and in the acute fevers. It is also brought about in a very pronounced form in poisoning by phosphorus and arsenic. In a minor degree it is seen in debilitating diseases, and is often the more immediate cause of death in hypertrophy of the heart.

Fig. 210. - Fatty degeneration of the heart. The muscle flecked with light spots.

The fatty degeneration usually shows itself in patches, so that the muscular tissue is seen to be, as it were, flecked with pale spots or streaks. This is best seen on examining the muscular tissue from within (see Fig. 210), as the endocardium generally produces but little obscuration of these markings, and they are most abundant in the inner layers of the muscular substance. This flecked appearance is not always present, and it would be a mistake to infer the absence of fatty degeneration from its absence. The heart again is generally flabby, friable, and pale in colour, but a very flabby heart may be very little fatty, and fatty degeneration may co-exist with a comparatively firm muscular tissue. Microscopic examination should therefore always be resorted to.

Under the microscope in those cases in which the degeneration is in patches, the transparent muscular tissue is seen with a low power to be interrupted by opaque patches, as in Fig. 211. The general outline of the muscular cylinders is preserved, but they are evidently replaced by some foreign material. Under a high power, as in Fig. 212, the individual fat drops become apparent. These fat granules are frequently seen to be in rows, representing the original muscular fibrillae, and the contractile substance is obviously lost or converted into oil. In minor degrees the degeneration is, as a rule, more uniformly distributed in the muscular substance, and we can see that the fat granules generally appear first in the neighbourhood of the nuclei of the muscular fibres, forming elongated collections extending from either pole of the nucleus.

Fig. 211. - Fatty degeneration of the heart. The occurrence of the lesion in patches is indicated by the dark appearance of the fibres, x 90.

Fig. 212. - Fatty degeneration of the heart. A single fibre with oil drops in it, as seen in the fresh state, x 350.

It is clear that muscular fibres which have undergone this transformation in its extreme form are incapable of recovering their original condition. The sarcous substance has undergone transformation. It is to be inferred, therefore, that when such a heart recovers there is an absorption of the fat and an actual new-formation of muscular tissue. This process must be a comparatively frequent one when we consider how common fatty degeneration is in severe anaemias aud in acute fevers. The fatty heart is usually a dilated one, even where there is no dilatation to begin with.