106 THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 



It may even be said that Meves's observations, instead of proving that the 

 mitochondria are transformed into collagenic fibrils, indicate that the two are 

 quite distinct; for if there is. as he assumes, a change in the chemical constitution 

 of mitochondria so that they do not stain with either iron hematoxylin or fuchsin, 

 one would expect to see some evidence of this in his figures. But his figures 

 show that the mitochondria are characterized by the extreme uniformity of their 

 reactions to iron hematoxylin; they show no variabihty whatever. Again, if, as 

 he further assumes, there is another change in the chemical constitution of the 

 invisible fibrils (invisible by his own assumption) by which they acciuire an intense 

 affinity for collagen-staining dyes, one would look for some variation in the stain- 

 ing with the said collagen dyes. But the figures show that there is no variation 

 in the reactions of the fibrils. The third point, which may be justly urged, is his 

 last assumption that in later stages the fibrils are differentiated by virtue of a 

 formative activity. It follows that the theory of the origin of the fibrils from 

 mitochondria is aiiplicable only to a very limited stage in their formation and does 

 not fit the facts which he himself has observed relative to their formation in older 

 embryt)S. 



The argument from analogy advanced by Duesberg (1912, p. 759), that the 

 formal proof of the role of mitochondria in the formation of myofibrils may be 

 regarded as indirect evidence of their participation in the develoi^ment of other 

 formed elements (collagenic fibrils and neurofibrils) cuts both ways; for it is etiually 

 true that the notable absence of evidence in favor of the formation of collagenic 

 fibrils by a transformation of mitochondria leads one to doubt a like origin of 

 myofibrils. 



MYOFIBRILS. 



Although Benda (1899rt, p. 379) and Meves (1907a, p. 402) were the first 

 investigators to claim that mitochondria became changed into myofil^rils, Dues- 

 berg (1909, 1). 126, and 1910, p. 647) has furnished the most complete evidence in 

 support of this contention. His material consists of a very complete series of 

 chick embryos of from 19 hours' to 10 days' incubation prepared by Benda's method 

 for mitochondria. He employed also, for control, subhmate acetic, alcohol, and 

 other fixatives, and the chloride-of-gold method of Ranvier. He studied both the 

 myotomes and the myocardium, but his most detailed work related to the former. 

 He found that at first the mesoblastic cells contain only typical mitochondria in 

 the form of granules, rods, and short, wavy filaments, and that in more advanced 

 stages of development filaments of the same girth and morphological characters 

 became more and more numerous and of greater and greater length, until they 

 began to show traces of differentiation into segments. The mitochondria and 

 the homogeneous filaments stained alike by the Benda method, but after the first 

 indications of segmentation appeared the staining reaction of the fibril began to 

 change, for they no longer stained as deeply as the mitochondria. His figures 

 indicate a marked decrease in the amount of mitochondria parallel with the differ- 

 entiation of fibrils. This is seen by a comparison of figure 14 with the succeed- 

 ing ones, figures 16, 20-23, 25, and 26. He arrived at the conclusion that the 

 mitochondria elongate and become transformed into myofibrils. 



