MITOCHONDRIA IN VERTEBRATE NERVE CELLS 13 



for instance. I find that they stain the mitochondria in embry- 

 onic nerve cells of vertebrates (chick), and in fully differentiated 

 nerve cells of invertebrates (edible crab, Callinectes hastatus) 

 much more brilliantly than the mitochondria in the spinal gan- 

 glion cells of the adult vertebrates which I have examined. 



The relative amount of mitochondria is apparently constant 

 in the nerve cells pf the different animals although there is a 

 certain amount of variation among the spinal ganglion cells of 

 the same animal, which could not be accurately determined on 

 account of the difficulty in enumerating them. The amount 

 of mitochondria illustrated in the figures would be more uniform 

 than it is were it not for this individual variation. Where the 

 mitochondria are few in number lipoid gi'anules are abundant 

 and vice versa. 



The relation of mitochondria to lipoid globules^ was studied in 

 detail in the guinea-pig, but a reciprocal relationship between 

 the relative amounts of the two was observed in all the animals 

 investigated. It is easy enough to distinguish typical mitochon- 

 dria (fig. 2, m) from typical lipoid (?) but it is impossible to 

 determine whether the intermediate stages (i) are true mito- 

 chondria or true lipoid. Coincident with the change in shape 

 from mitochondria to lipoid there is a progressive increase in 

 the resistance to acetic acid. The mitochondrial methods show 

 no difference between the fixation and stainirg properties of 

 mitochondria and lipoid, but the lipoid globules are not so 

 readily destroyed by fixation in Carnoy's fluid and Zenker. By 

 varying the concentration of the acetic acid in Zenker's fluid 

 a series of gradations may be obtained in spinal ganglion cells 

 of the pigeon between lipoid and no mitochondria, on the one 

 hand, and lipoid plus the normal amount of mitochondria, on 

 the other. Both mitochondria and lipoid stain with nilblau B 

 extra in the cells of all the animals, but the actual transforma- 

 tion of the one into the other could not be followed. Probably 



■* I have applied the term 'lipoid' (derived from the Greek, Xiiros, fat) to these 

 globules, loosely, without meaning to convey any exact knovvlege of their 

 composition. It is possible that their composition may differ in the various 

 animals which I have studied. 



