THE SIXO-VENTKICULAK SYSTEM 165 



the injected fluid may ha^'e hel])ed to form these clefts yet it is 

 interesting to note that the clefts always occur between tlie 

 presumed cell boundaries and never extend into the cells. The 

 weak points in the fasciculus seem to be in the intra-cellular 

 region. Small canals entering the fasciculus were occasionall,y 

 observed to be injected. Figure 13 shows such a small injected 

 canal. They end l)lindly and seem to be similar to the clefts, 

 i. (\, inter-cellular in nature. 



DeWitt regards the bundle as syncytial in structure. She bases 

 her conclusion on: 1) the constant presence and continuation 

 of the fibrils in the system, thus making the fibril the unit of the 

 system. 2) the absence of any connective tissue penetrating 

 the S.\'.S. cells and 3) believes that the clefts mentioned by 

 Tawara are caused l)y shrinkage tlui'ing fixation. However, 

 Tawara, in s])ite of the continuation of fibrils throughout the 

 fasciculi, considers the system as being made up of independent 

 cells for he noticed wavy lines which he believed to be the out- 

 lines of the cells and at times also observed clefts between the 

 cells. 



The results obtained incidentall.y by use of the injection 

 method and by teasing seem to show beyond all doul)t that in 

 the beef heart the 8.A\S. is made up of independent cells. The 

 injection of the clefts with injection mass and the reduction of 

 silver nitrate by the intercellular substance seems to offer con- 

 firmatory evidence in regard to this conclusion. 



The technique used for microscopic study of the injected sheath 

 and fasciculi was as follows: The endocardium was stripped 

 from the injected region, thus leaving the injected fasciculi on 

 the myocardium. A portion about one centimeter long was 

 then cut out and laid face downwards on a slide. The myo- 

 cardium was scraped off and nothing but the injected fasciculi 

 and the inter\Tning connective tissue and fat were left on the 

 slide. A drop of glycerine and a cover glass were added and the 

 preparation was ready for examination. This simple method 

 affords a quick and, for some things, satisfactory method for 

 studying the results of injection of any kind into the sheath. 



By making microscopic examinations of fasciculi injected with 

 Prussian blue it was interesting to note that exti'avasation into 



THi; \.M10RIC\N JOUHNAl, OI' AXATO.MY, VOL. 11). NO. 2 



