MITOCHONDRIA IN VERTEBRATE NERVE CELLS 9 



gation. It was that with the specialization of the embryo into 

 different organs and tissues, primitively similar cells assume 

 special functions which find expression 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 constituent, the chon- 

 driosomes (mitochondria). Thus the neurofibrils are, accord- 

 ing to his conception, to be classified as products of mitochondria. 

 Hoven's ('10, p. 475) work on the transfonnation of mitochon- 

 dria into neurofibrils in the developing nerve cell has generally 

 been accepted (Firket '11, p. 545; Arnold '12, p. 289, and others) 

 as a ratification of Meves' hypothesis, although Duesberg ('12, 

 p. 745), under whose direction Hoven did his work, does not 

 claim that he demonstrated his point conclusively. Since it 

 was supposed that the mitochondria became transformed into 

 neurofibrils, it was natural to believe that mitochondria are 

 absent in the adult nerve cell after neurofibril formation has 

 ceased. Thus we find that Meves ('10, p. 655), Duesberg (10, 

 p. 612) and Hoven ('10, p. 478) have expressed their opinion 

 that there are no mitochondria in fully developed nerve cells. 

 Consequently investigators have looked for them and failed to 

 find them. I repeated Hoven 's work and found that the facts 

 do not justify his conclusion that mitochondria become trans- 

 formed into neurofibrils (Cowdry '14 a, p. 414). Now that a 

 reaction is taking place against Meves' hypothesis (vide Gure- 

 witsch '13, p. 126; Levi, '13, p. 550; Cowdry '14 a, p. 409, etal.) 

 we may look forwa.rd to the study of mitochondria in nerve cells 

 receiving the attention which it certainly merits. 



MATERIAL AND METHODS 



This investigation has been limited to spinal ganglion cells. 

 Spinal ganglia were selected because they are easy to obtain, 

 fluids penetrate them rapidly and because I believe that they 

 constitute suitable material for experimental studies. All the 

 animals, with one exception (Homo), were adults. The sex of 

 the animals and the dates of the observations are recorded. 

 Sizes were estimated by inserting, in the ocular, a micrometer 



