22 H. HAYS BULLA RD 



degeneration' as involving in certain cases both the myocardium 

 proper and the His bundle, in other cases he finds droplets only 

 in the cardiac fibers, in still others the bundle alone is affected. 

 According to Engel ('10) there is usually more fat in the fibers 

 of the bundle than in the myocardium proper. Sternberg ('10) 

 has been able to observe no difference in this respect while 

 Monrad-Krohn ('11) has found the heart muscle invariably more 

 fatty than the Purkinje fibers. 



In the literature I have found but a single reference to an ex- 

 amination for fat of the atrio-ventricular system in the lower 

 animals. Engel ('10) reports that she was unable to demon- 

 strate any fat in the Purkinje fibers of the pig and sheep. Most 

 of the observers just cited have examined frozen sections, from 

 the interventricular septum, a short distance below the aortic 

 valve, showing both the myocardium and the left limb of the 

 bundle. With respect to the fat content of the Purkinje fibers 

 such sections may usually be regarded as typical of the bundle 

 as a whole. The observations recorded in tables 4, 5, 6, 7 and 8, 

 have reference to sections from the region just indicated. I 

 have also frequently examined sections of the right limb and 

 of the end branchings of both limbs. In a few cases the muscle 

 fibers of the sino-auricular node and of the atrio-ventricular node 

 were also examined. I have not studied the bundle of His in 

 rats for the reason that it is small and in frozen sections it is 

 frequently difficult to distinguish the muscle fibers of the bundle 

 from the cardiac fibers. With other animals this difficulty was 

 not experienced. 



Sheep, hog and ox. Figure 9 represents a transverse section 

 from the moderator band of a hog (no. 104, table 7). The Pur- 

 kinje fibers, P, contain a much smaller amount of fat than the 

 cardiac fibers, D and L. In the sheep, hog and ox, as is well 

 known, the fibers of the atrio-ventricular system are of the typi- 

 cal Purkinje type and morphologically they differ widely from 

 ordinary cardiac muscle. In these animals (table 7) the Pur- 

 kinje fibers and muscle tissue of the atrio-ventricular node and 

 of the sino-auricular node, contain normally but a very small 

 amount of fat. As shown in the tables, this is the case even 



