410 E. V. COWDRY 



embryos (figs. 1 and 2). Held also has demonstrated mitochon- 

 dria by both the Altmann method ('97, figs. 1 and 2) and the 

 iron hematoxylin technique ('97 a, fig. 10) in adult ner\'e cells. 

 In addition I, myself, have shown (1912 a and 1912 b) that mito- 

 chondria are present in large numbers in adult spinal ganglion 

 cells of the pigeon. 



(2) The second statement postulates the existence of three 

 distinct phases in the developing neurofibril, each of which is 

 characterized by certain microchemical properties. In the 

 first stage the primitive neurofibrils may, it is said, be stained by 

 mitochondrial methods, in the second by both mitochondrial 

 and neurofibrillar methods and in the third by the ^-arious 

 neurofibrillar methods of technique alone. 



I find that neurofibrils in chick embryos may be stained by 

 such mitochondrial methods as the iron hematoxylin method of 

 Aleves (fig. 4), Benda's method, the anilin fuchsin methylene 

 blue erythrosinate (fig. 27) and the anilin fuchsin toluidin blue 

 (figs. 21, 26 and 25) methods, of Bensley; but the staining is not 

 specific and seems to depend upon the degree of differentiation. 

 A comparison of figures 21, 26 and 25 will show that this is the 

 case with respect to the last mentioned method. These three 

 figures ha^'e been drawn from neighboring sections of the same 

 embryo, mounted on the same slide and prepared by Bensley's 

 anilin fuchsin toluidin blue method. In the first (fig. 21) the 

 differentiation is practically nil, the mitochondria staining ex- 

 actly the same color as the neurofibrils; in the second (fig. 26) 

 it has been carried a little further with the result that the neuro- 

 fibrils have lost their bright crimson color and have assumed a 

 dull red shade; while in the last (fig. 25) the decolorization has 

 been carried to an extreme so that the neurofibrils have lost all 

 of the acid fuchsin and have become stained with the differentia- 

 tor, toluidin blue. It is to be noted that, in these progressi^-e 

 stages of differentiation, the initial affinity of the neurofibrils for 

 an acid dye (acid fuchsin) in which they resembled mitochondria, 

 is gradually changed to an affinity for a basic dye (toluidin blue) , 

 while the intensit}^ of the coloration of the mitochondria with 

 the acid fuchsin remains unaltered. Furthermore, the fact that 



