CYTOPLASMIC CONSTITUENTS OF NERVE CELLS 405 



stains evenly throughout. It is in this distal, highly colored, por- 

 tion of the cytoplasm that the neurofibrils are later first completely 

 differentiated. It should be noted, in passing, that certain 

 portions of the cells of the adjacent myoblasts likewise stain a 

 similar dark yellowish brown color with silver nitrate. 



4. Comparison of mitochondria and neurofibrils in embryological 

 series: embryos of 19 to 31 somites 



It has already been mentioned that we have not at present 

 a technique at our disposal by means of which the mitochondria 

 and neurofibrils may be stained differentially in the same cell in 

 a constant and trustworthy fashion. For this reason a synthesis 

 must be resorted to. With this in mind I have endeavored to 

 build up a synthetic picture of mitochondria and neurofibrils as 

 they appear in cells of increasing degrees of differentiation. Two 

 series of embryos extending from stages of 19 to 31 somites, each 

 member of a series differing from the preceding by the acquisi- 

 tion of a single mesodermic somite, were employed, one being 

 prepared by Meves' iron hematoxylin method for mitochondria 

 (figs. 15 a, etc.) the other by Cajal's silver nitrate method for 

 neurofibrils (figs. 15 b, etc.). Four additional methods of tech- 

 nique were used for control, namely, janus green intravitam, Bens- 

 ley's aniUn fuchsin methyl green method, the Benda method 

 and Paton's modification of the Bielschowsky silver impregna- 

 tion technique. All embryos were cut in complete serial trans- 

 verse sections. In making the comparisons morphological equiv- 

 alents (of approximately the same area and thickness, 4 ix) alone 

 were used, or, in other words, cells occurring on the right side 

 of the neural tube opposite the sixth somite in embryos of the 

 same degree of differentiation. The two chief parallel series, 

 which are in part represented in plates 3 and 4, afford a fairly 

 secure basis for the comparison of the form, distribution, stain- 

 ing reactions and relative amount of mitochondria and neurofibrils 

 in developing nerve cells. 



a. Form. The shape of mitochondria is, to some extent, de- 

 termined by the configuration of the cells containing them. Thus 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 15, NO. 4 



