THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 107 



Von Kurkiewicz arrived at the same conclusion concerning the mitochondrial 

 origin of the fibrils in the heart-muscle of the chick. Schultze also claims to have 

 confirmed Duesberg's contention regarding the role of mitochondria in myofibril 

 formation. Brlick (1914, p. 581) has described the mitochondrial origin of myo- 

 fibrils in Anodonta cellensis. Moreover, Leplat (1912, pp. 458 and 509) has studied 

 the development of fibrils in Mm. sphincter pupilla? and ciliaris of birds by the 

 application of the Benda method. He was able to observe all the stages in the 

 differentiation of the myofibrils which Duesberg described and he reaches the same 

 conclusion. The following additional investigators favor the doctrine of the trans- 

 formation of mitochondria into myofibrils: Lewitsky (1910, p. 539), Favre and 

 Regaud (1910, p. 1138), Hoven (1910a, p. 476), Prenant (1911a, p. 463), G. Arnold 

 (1912a, p. 289), Schiifer (1912, p. 193), Luna (1913f, p. 478), Jordan and Ferguson 

 (1916, p. 94), and others. Heidenhain (1911. p. 1086), Levi (1911, p. 191), and 

 Gurwitsch (1913, p. 123) are in the minority in that they do not subscribe to it. 



The accuracy of the facts forwarded by Duesberg being beyond cavil, it 

 becomes necessary for us to determine whether they permit of any other interpre- 

 tation except that advanced by him. The nature of the unsegmented fibrils and the 

 significance of the fluctuations in the amount of mitochondria are important points. 

 Apparently the technique employed is not specific, for it colors the mitochondria 

 and the primitive fibrils in the same way, although they differ in their microchemi- 

 cal properties, because we find that the mitochondria are dissolved by fixatives 

 containing a concentration of acetic acid which in no way affects the myofibrils. 

 They also react differently to stains. If, therefore, differences of this nature are 

 not revealed by the technique employed, the possilMlity must be entertained that 

 the elongated homogeneous filaments described by Duesberg may differ inter se; 

 in other words, that we may be dealing with two different kinds of filaments which 

 may appear similar on account of the stain which is used, one of which is mito- 

 chondrial, the other a precursor of the definitive myofibrils which does not possess 

 the properties of mitochondria; so that Duesberg's investigations do not exclude 

 the possibility of the origin of myofibrils from material which is not mitochondrial. 

 In fact, there is some indication of the existence of non-mitochondrial precursors. 

 I refer, for instance, to the observations of Godlewski (1902, ix 149) and others, 

 according to which the myofibrils result from the confluence of small masses of 

 material, not through the elongation and transformation of a homogeneous filament. 



Moreover, I have observed in my own preparations of chick embryos of 100 

 hours' incubation (stained with fuchsin and methyl green) very delicate green- 

 colored fibrils, side by side with others stained red, and still others beginning to show 

 traces of segmentation. I have also seen similar fibrils stained red with alizarin 

 in Benda preparations and light gray with iron hematoxylin. Morphologically 

 they resemble the filamentous mitochondria, but their staining reactions are entirely 

 different. Whether they give rise to the definitive fibrils or not I can not say. 



Duesberg (1915, j). 59) has sujiplemented his discovery of the abundance of the 

 mitochondria in the myoblasts and their subsequent diminution during fibril for- 

 mation by important investigations on ascidians, where he found that the mitochon- 



