434 E. V. COWDRY 



they become transformed into fibrils and other products of dif- 

 ferentiation, but the trouble is that the ways of nature are not 

 simple, that the obvious interpretation is not necessarily the 

 correct one. 



In looking over the literature one is confronted with an appall- 

 ing mass of conflicting observations, no unanimity is evident, 

 as was seen in the work on the chemical constitution of mito- 

 chondria. Certain investigators have overstepped the mark. 

 For example, mitochondria were seen and described in adult 

 nerve cells by Altmann ('90, p. 52), Levi, ('96, p. 3), Nageotte 

 ('09, p. 827) and others. Hoven in 1910 arrived at the con- 

 clusion (p. 475) that the mitochondria are transformed into 

 neurofibrils in the developing nerve cell. This was generally 

 accepted (Firket '11, p. 545 and Arnold '12, p. 289). Since it 

 was supposed that mitochondria become transformed into neuro- 

 fibrils it was natural to think that they were absent in the adult 

 nerve cell after neurofibril formation has ceased. Meves ('10, 

 p. 655), Hoven ('10, p. 478) and certain others expressed this 

 opinion, and it fell to my lot to rediscover mitochondria in the 

 nerve cell ('12, p. 497) and to show that the evidence is not 

 conclusive that they become changed into neurofibrils ('14a, 

 p. 416). 



But critical mention need only be made of the claims that 

 mitochondria transform into hemoglobin (Schridde '12, p. 517), 

 pigment (Asvadourova '13, p. 293), coUagenic fibrils (Meves^ 

 '10, p. 150), zymogen granules of the pancreas (Hoven '10a, 

 p. 350), goblet cell-mucus (Grynfeltt '13, p. 10) and to the sug- 

 gestion of the same author that they also form the colloid sub- 

 stance of the thyroid gland ('12, p. 147). 



The evidence is based chiefly upon similarities in form, which 

 do not mean very much, and upon similarities in the staining 

 reactions of fixed tissues, which mean still less. Moreover, 

 hemoglobin, and the variety of pigment mentioned by Asva- 

 dourova, are both chromoproteins, one having the pyrrol 

 nucleus and the other containing tyrosin; while collagenic fibrils 



^ Moves line of reasoning is interesting as well as unanswerable for he assumes 

 that the mitochondria are invisible (not staining with either iron hematoxylin or 

 fuchsin) when they form the fibrils (p. 164.) 



