156 



Mr. J. G. Wilson. 



[Jan. 21, 



my observations to the main bundle surrounded by its connective tissue 

 sheath, including the part directed to the coronary sinus and the two arms 

 running into the septal walls of the right and left ventricles (figs. 1 and 2). 

 My results have been obtained by the methylene blue " vital " method. 

 Occasionally the Cajal method or gold impregnation was used, but with 

 results less satisfactory, chiefly, I believe, because the methylene blue gave 

 such definite results that it was not felt necessary in this preliminary report 

 to ascertain experimentally the modifications which appeared necessary to 

 apply either of these methods, especially the Cajal, to the heart muscle. 

 The strength of the solution injected was : — 



The coronary arteries were injected with the solution either directly or 

 indirectly from the aorta. When the heart was well injected the bundle was 

 rapidly dissected out, placed on a slide and examined in the usual way ; or 

 the bundle was cut out from the fresh heart, partly immersed in a methylene 

 blue solution slightly weaker than the above, and kept in a hot chamber at a 

 temperature of 37° or 38° C. The full description of the technique in use has 

 been so often presented in previous papers, Wilson (8), that it seems 

 unnecessary to repeat it here. Fixation was always done in 8-per-cent. 

 ammonium molybdate and sections cut in paraffin. 



The limitations of the methylene blue technique are well known. This dye, 

 though neurotropic, is not monotropic. A difficulty encountered in the atrio- 

 ventricular bundle is the affinity of the methylene blue for the elastic fibres — 

 a tissue sufficiently abundant in the bundle to give trouble at first. 

 Kecognising this possible source of error, one readily gets accustomed to 

 distinguish between the relatively coarse wavy fibres of the elastic tissue and 

 the fine varicose fibres of the nervous strands branching and anastomosing 

 irregularly. 



The nerve fibres are in the main non-myelinated. A few medullated 

 fibres are to be seen, especially in the calf : these appear usually as isolated 

 fibres and do not enter as a rule into the strands of fibres which pass directly 

 through the bundle. 



The staining of all the nerve elements in the bundle in one and the same 

 preparation is unusual. Thus it is not common to get in the same prepara- 

 tion the finer network together with the ganglion cells and their processes- 

 If one gets good ganglion cells with processes, the finer varicose fibres 

 distributed through the muscle are usually poorly stained. This agrees with 

 the observations which I have satisfied myself with time and again, that the 



Methylene blue, J-per-cent. solution 

 Salt solution, 09-per-cent. solution . 



10 c.c. 

 90 „ 



