THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 101 



amount of vitellus and few if any mitochondria. A similar quantitative relation 

 between mitochondria and fat has been noted by many authors, and I have par- 

 ticularly in mind the observations of Goetsch (p. 13G). We know that decrease in 

 oxidation causes the deposition of fat and we suspect that mitochondria are actively 

 concerned in oxidation (p. 134). It is common knowledge that they are particu- 

 larly abundant in active cells, which must be respiring at a rapid rate. In other 

 words, the heaping-up of fat and the diminution in the mitochondria indicate 

 reduced oxidation; and conversely, the absence of fat and the abundance of mito- 

 chondria indicate an increase. Accordingly it is possible that the distribution of 

 these substances, as described by Conklin and Duesberg, is merely the visible mani- 

 festation of differences in the rate of oxidation in different parts of the egg and in 

 the different tissues of the embryo. 



HISTOGENESIS. 



The origin of the idea that mitochondria are concerned with histogenesis is 

 not difficult to trace. They occur in all embryonic cells. In early stages of 

 development they are the only formed elements in the cytoplasm. They are fila- 

 mentous in the mj'obla.sts and neuroblasts, and it is perfectly natural to think that 

 they become transformed into fibrils and other products of differentiation; but the 

 trouble is that the wa,ys of nature are not simple, that the obvious interpretation 

 is not necessarily the correct one. It also falls in line with the view that they con- 

 stitute the material basis of heredity (p. 98). Meves (1908, p. 845) writes that, 

 with the specialization of the embryo into different organs and tissues, primitively 

 similar cells assume special functions which find expre.ssion in characteristic struc- 

 tures or differentiations. All these products, no matter how heterogeneous they 

 may be, arise through the metamorphosis of one and the same elementary plasma- 

 cortstituent, the chondriosomes. Thi.s is a very sweeping statement, but even it 

 does not express the situation correctly, because claims are also made that most of 

 the products of the activity of speciahzed cells of the adult organism, like secretion 

 granules, are also formed by a chemical transformation of mitochondria. 



The dominating influence of this dogma has made itself felt in many ways. 

 To cite a single instance, Hoven in 1910 arrived at the conclusion that mitochondria 

 are transformed into neurofibrils in the developing nerve-cell. This was gener- 

 ally accepted (Firket, 1911, p. 545; G. Arnold, 1912a, p. 289, and others). Fol- 

 lowing this line of reasoning, Hoven, (1910a, p. 478) and Meves (19106, p. 655) 

 concluded that the mitochondria are absent in adult nerve-cells after neurofibrillar 

 formation has ceased, and looked for them and failed to find them. And this in 

 spite of the fact that Altmann (1890, p. 52), Levi (1896, p. 180), Lobenhoffer (1906, 

 p. 491), Nageotte (1909, p. 827), and others had already clearly and precisely 

 figured and described them. 



In order to get a true conception and perspective of what these claims really 

 mean, I have tabulated some of the structures which are said to be developed 

 through the transformation of mitochondria or under their influence. 



