FAT AND MITOCHONDRIA IN CARDIAC MUSCLE 21 



few if any of the organs of the body are chemically fat free and 

 that visible fat is normally present in many of the parenchyma- 

 tous cells including nearly all of the gland cells and the skel- 

 etal muscle fibers. In these active tissues there is normally a 

 variable quantity of visible fat which represents the reserve be- 

 tween intake and utilization. The experimental observations 

 here recorded clearly indicate that in cardiac muscle fibers a 

 certain visible reserve of fat is normal and this reserve may 

 at times appear surprisingly large without pathological signifi- 

 cance. In reality the fat reserve, in proportion to the great 

 amount of work done by the heart, is at all times very small. 

 Under normal conditions the sugar of the blood, often stored 

 as glycogen in cardiac muscle, is known to be the chief source 

 of the energy of the heart beat. 



OCCURRENCE AND SIGNIFICANCE OF NEUTRAL FAT IN THE 

 MUSCLE TISSUE OF THE ATRIO- VENTRICULAR SYSTEM 



Fatty degeneration of the muscle fibers of the His bundle 

 has been reported in fatal cases of diphtheria by Amenomiya 

 ('10), Sternberg ('10), Monrad-Krohn ('11), and Tanaka ('12). 

 Monckeberg ('08) definitely rejects the possibility that visible 

 fat in the Purkinje fibers may be normal, and advances the idea 

 that fatty degeneration of the His bundle is frequently ' the ana- 

 tomical expression of the immediate cause of death.' Engel 

 ('10) who examined eighty-nine human hearts has made a more 

 detailed investigation of this question than any yet attempted. 

 In the human fetus, in children, and in young individuals she 

 found no fat in the Purkinje fibers but in individuals past 

 forty years of age the fibers invariably contained fat. Engel 

 believes the fatty condition somewhat pathological, but con- 

 siders it of slight clinical significance since the function of 

 the conductive system is not impaired. AschofT ('10) holds 

 similar views. 



It is well-known that the muscle tissue of the atrio-ventricular 

 system has 'a certain physiological independence, in part, due to 

 an independent and abundant blood supply as well as an inde- 

 pendent nerve supply. Monckeberg ('08) has described 'fatty 



