THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. Ill 



said, be stained by mitochondrial methods; in the second by both mitochondrial 

 and neurofilirillar methods; in the third by the various nevu-ofibrillar methods 

 of techni(iLie alone. I have found (and I have already described the fact) that 

 structures which we are accustomed to call neurofibrils may in truth be stained 

 by certain mitochondrial methods. I refer to the iron-hematoxylin method of 

 Meves, the Benda method, and the anilin fuchsin methylene-blue erythrosinate and 

 toluidin-blue methods of Bensley, but the staining is not specific and depends on 

 the degree of differentiation. A comparison of figures 21, 26, and 25 published 

 in my 1914d paper will be sufficient to show that this is true in the case of the 

 last-mentioned method. These three figures have been drawn from neighboring 

 sections of the same embryo of 100 hours' incubation, mounted on the same slide, and 

 stained with anilin fuchsin and toluidin blue. In the first figure, the differentia- 

 tion is practically nil, the mitochondria staining exactly the same color as the 

 neurofibrils; in the second figure it has been carried a little further, with the result 

 that the neurofibrils have lost their bright crimson color and have assumed a dull 

 red shade; wdiile 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 differentiator, toluidm blue. It is to be noted that in these pro- 

 gressive stages of differentiation the initial affinity of the neurofibrils for the acid 

 dye (acid fuchsin), in which they resembled mitochondria, is gradually changed 

 to an affinity for a basic dye (toluidin blue), while the intensity of the coloration 

 of the mitochondria with the acid fuchsin remains unaltered. Furthermore, the 

 fact that the coloration of the neurofibrils by mitochondrial dyes is marked in adult 

 cells, which I have mentioned in a preceding contribution, should be taken into 

 consideration before regarding it as indicative of the existence of transitions 

 between mitochondria and primitive neurofibrils. 



Let us now consider the statement that the primitive neurofibrils may be 

 stained by both the mitochondrial and the neurofibrillar methods (i. e., the second 

 phase). The completeness of the demonstration of mitochondria by the iron- 

 hemato.xyUn method depends upon the presence in the fixative of chromic acid, 

 osmic acid, and acetic acid, in suitable amounts, and on the mordanting action of 

 iron alum, while theu- complete absence in the neurofibrillar preparations is due 

 to the unmodified action of silver nitrate. The neurofibrils seem to have a special 

 affinity for silver nitrate, upon which all silver impregnation methods depend. 

 So it is extremely unhkely, especially in the absence of direct evidence, that so 

 widely divergent methods stain the same thing, namely, the primitive neurofibrils. 

 Of course it will be argued by the adherents of this theory that the Italian inves- 

 tigators have succeeded in demonstrating mitochondria by modified Golgi methods, 

 but there is a long step between this fact and proving that the mitochondria in a 

 certain specified stage in the developing nerve-cell may be stained interchange- 

 ably by mitochondrial and neurofibrillar methods. If this should be the case in 

 other stages when neurofibrils are not being formed, and in other tissues, it would 

 of necessity be deprived of the significance which investigators have been incUned 

 to attach to it. 



