FAT AND MITOCHONDRIA IN CARDIAC MUSCLE 23 



when the cardiac muscle of an individual contains a large fat de- 

 posit. In the papillary muscles of the sheep's heart I have sev- 

 eral times been able to trace the transition fromPurkinje fibers to 

 typical cardiac fibers. On passing from the former type to the 

 latter the fibers become increasingly fatty. The droplets in the 

 Purkinje fibers are frequently most numerous in the sarcoplasm 

 immediately surrounding the nuclei, or they may be scattered 

 throughout the fibers or may occur in groups or clusters. 



Dogs. Figure 10 shows a section from the left limb of the 

 bundle in a dog (no. 90, table 6). Cardiac fibers are marked 

 D and L, Purkinje fibers, P. A section of the atrio-ventricular 

 node of the same heart is shown in figure 12 and of the sino- 

 auricular node in figure 11. In the hearts of the six dogs listed 

 in table 6 the Purkinje fibers contain somewhat less fat than 

 the cardiac fibers but more than the fibers of the nodal tissue. 



Cats. In figure 6 at P are seen a few fibers from the left limb 

 of the His bundle of a cat (no. 84, table 3). Cardiac fibers are 

 shown at C. The amount of fat in the Purkinje fibers in this 

 individual is less than in the cardiac fibers. Of the thirty cats 

 listed in tables 4 and 5, eight have more fat in Purkinje fibers 

 than in cardiac fibers, six have more in cardiac fibers, while in 

 sixteen individuals the amount in the two systems is approxi- 

 mately equal. I have not examined the nodal tissue of the heart 

 in cats. 



Hujnan. Figure 7 shows fat in the cardiac fibers and His 

 bundle of an eight months human fetus. Table 8 gives an idea 

 of the fat content of the Purkinje fibers of five human fetuses. 

 Two children, one of eleven months (congenital syphilis) and one 

 of three years (empyema) are also listed in the table. I have ex- 

 amined the conductive system in only six adult human hearts. 

 Fat was found in the muscle fibers of the bundle in each case 

 and in two individuals the amount was very large. Figure 8 

 represents a section from the interventricular septum of the 

 heart in a fatal case of lobar pneumonia occurring in a negress 

 aged fifty-three. No doubt the conditions represented in the 

 figure would usually be regarded as decidedly pathological. 

 From the observations of Engel ('10) and Aschoff ('10), however, 



