482 DAVID H. DOLLEY 



While I have thus attempted to give in detail the presumptive 

 sequence of the development of cytoplasmic pigment, it must 

 not cloud by its theoretical element the primary objective fact 

 that cytoplasmic pigment is associated in its origin with obvious 

 nuclear materials in the inclusive sense. 



The beginning of a generalization for pigmentation of the 

 nervous system may be made. Broadly, it necesarily falls into 

 two groups, the normal and the abnormal. Of normal pigment 

 in the sense of a constant morphological structure, the sub- 

 stantia nigra, the locus coeruleus, and certain other cells con- 

 stitute examples. 



A discussion of these is beyond the scope of this paper, but at 

 least a suggestion may be ventured. Nerve cells as a class possess 

 universally a chromidial apparatus ordinarily called the Nissl sub- 

 stance. The relation of such ^n organelle to pigment formation 

 becomes clear in a cell where pigment formation is the specialized 

 function as in the dermal chromatophore elucidated by Schultz. 

 Is not pigment formation when it is a normal structure to be 

 correlated with some such differentiation in the nerve cell? This 

 would include all normal pigment as phases of differentiation. 

 Of course, the reference here and elsewhere is to autochthonous 

 pigmentation, not to accidental pigmentation, such as the 

 hematogenous. 



Excluding all normal pigmentations, the preliminary generali- 

 zation for the abnormal autochthonous group seems reasonably 

 clear. It is a phenomenon of chronic depression, or depressant 

 senility. It is not a phenomenon of normal functional activity, 

 so far as the Purkinje cell represents the typical reaction of a 

 chromidial apparatus. 



Normal function and depression together include the possi- 

 bilities of reactions of irritability, in other words, the whole 

 range of reactions of the specialized nerve cell. Pigment has 

 never come to notice in the ordinary routine in normally function- 

 ing Purkinje cells, nor particularly in naturally senile cells where 

 it has been the object of special search. This corresponds to the 

 statement of Marinesco ('09, p. 288) for the cerebellum. It 

 would not be expected to be, for such a type cell even t;o senility 



