152 THE SINO- VENTRICULAR BUNDLE. 



The description just given applies only to the pig's heart. Similar conditions 

 will be found in other Ungulata, but in the heart of man and of Carnivora one would 

 have difficulty in recognizing the cellular multiplications just described. The 

 first thing we have to consider is that in the Carnivora there are but two nuclei to 

 a heart-muscle cell, while in the pig there are eight. In the production of an adult 

 human cardiac muscle-fiber we would see but one-fourth as many nuclear divisions 

 as we do in the pig. These nuclear divisions seem to be restricted to the first and 

 second part of the bundle and to the Pur kin je fibers. The appearance in the human 

 is, therefore, not as striking as it is in the Herbivora. 



The cytologic details of the various parts of the bundle do not differ as markedly 

 as one might expect from the low-power examination. As in cardiac muscle, we 

 must distinguish three parts of the cell: the fibrils, the sarcoplasm around the 

 fibrils or sarcostyle, and the perinuclear sarcoplasms. 



It has been previously pointed out that it is not difficult to trace the bundle 

 from Tawara's node to the Purkinje fibers in sections that have been stained with 

 hematoxylin and van Gieson stain, or with Mallory's connective-tissue stain, 

 because these stains bring out the fibrous investment of the bundle very clearly. 

 One of these stains has been used by every pathologist who has reported on the 

 histological findings of Stokes-Adams disease. Many will admit that they would 

 be absolutely at a loss if they were to use a general stain, such as hematoxylin and 

 eosin. Further, it is evident that thick sections studied with the low powers of the 

 microscope make tracing of the bundle easier than thin sections with oil immersion. 

 The reason lies in the fact that the differences, in the human heart especially, 

 between the bundle cells and normal cardiac muscle cells are so slight that they 

 become evident only when seen en masse. The optical difference is primarily due 

 to a proportionately larger amount of sarcoplasm in the bundle fibers than there is 

 in the musculature. Sarcoplasm does not stain as heavily as do fibrils, with the result 

 that the bundle always stands out in thick sections as a light-colored area. It is 

 obvious that the thinner the section the more do these color differences disappear. 



I have endeavored to analyze the chemical nature and the cytologic details of 

 the sarcoplasm because I felt that an analysis of this cell element would give us a 

 clue as to the nature of the bundle. I attempted to determine the glycogen, lipoid, 

 and protein content and the mitochondria. I regret to say that I was only partly 

 successful. As regards the glycogen content, we confirm the work of Aschoff (1908), 

 who finds but very small amounts in the pig's heart. It should be noted, however, 

 that in the heart of beef and sheep the glycogen content far exceeds that of the 

 ventricular musculature. Indeed, it is not difficult to trace the course of the 

 bundle by means of the glycogen reaction. The reason the pig's heart has so little 

 is due to the fact that the nodal tissue which is restricted to the second part of the 

 bundle extends far into the ventricles. The sarcoplasm is much reduced. The 

 results in the heart of the rat were negative, but as only two hearts were examined 

 I do not consider them conclusive. The preponderance of evidence (see results 

 and discussions by Engel, 1910, and Aschoff, 1908) lies in favor of the view that 



