20 H. HAYS BULLARD 



upon fats the number and size of droplets in the cardiac fibers is, 

 within a few hours, increased to such an extent as to present a 

 picture which some would describe as marked fatty degeneration 

 (fig. 4). There is, however, no evidence of degenerative change. 

 The same general conditions no doubt apply to all laboratory 

 mammals. 



Either directly or by implication I have here offered the fol- 

 lowing reasons in support of the idea that visible droplets of neu- 

 tral fat are of physiological occurrence in the cardiac muscle 

 fibers of mammals: 1) In each of several well known species here 

 studied visible fat is found with great regularity in the heart 

 muscle of all individuals whether fetal, young or adult. Very 

 few, if any, of the cardiac fibers are absolutely fat free. 2) The 

 fat droplets are not found in the contractile elements. They 

 occupy a definite position in the sarcoplasm and do not interrupt 

 the continuity of Krause's membranes. 3) There are found in the 

 muscle fibers neither degenerative changes nor other evidence of 

 any pathological alteration of structure. 4) There is no evi- 

 dence of functional disturbance of the cardiac muscle. 5) The 

 quantity of fat is variable, is decreased in inanition and increased 

 by fatty foods. 6) Fat in cardiac muscle, with respect to general 

 occurrence, cytological relations and relation to nutrition, is close- 

 ly similar to that in skeletal muscle. An increasing number of 

 observers now regard the occurrence of visible fat in the latter 

 type of muscle as normal. 



It is well established that microscopically visible fat in cardiac 

 muscle is sometimes pathological. The mottled 'degeneration' 

 causing the well known tiger lily, tabby cat or thrush breast 

 appearance is an example. Those who insist that microscop- 

 ically visible fat in the heart is invariably of pathological signifi- 

 cance base their claim not so much upon any observed derange- 

 ment of cell function or degenerative change in cell protoplasm 

 as upon the assumption that normally the intake of fat is at all 

 times exactly balanced by utilization. Does this balance actu- 

 ally exist? Until recently such a balance was assumed in all the 

 parenchymatous cells of the body, those of adipose tissue and the 

 suprarenal alone being exceptions. It is now well known that 



