480 DAVID H. DOLLEY 



tumors derived from nonpigmented cells. Again in their work 

 the process emanated from a state of depression. 



For cells characterized by chromidial apparatus, the obser- 

 vations of Schultz ('12) on the formation of pigment in the dermal 

 chromatophore are especially illuminating and conclusive. Schultz 

 regards the chromatophore as a "highly differentiated cell whose 

 normal function is the formation of pigment; the process is the 

 result of specialized physiological activity." The process begins 

 in the undifferentiated mesoblastic cell by the extrusion of chro- 

 matin leading to the formation of a functional chromidial net. 

 Later the chromatin in the cytoplasm becomes changed into a 

 material which has the staining reactions of nucleolar substance. 

 Further change leads to the transformation of this material into 

 pigment. However, Schultz believes that probably specialized 

 plasmatic agents, chemical or catalytic, take part in this trans- 

 formation in the specialized chromotophore, because none or a 

 very small proportion of the extruded chromatin is transformed 

 into pigment in other cells. 



The parallel between the process in the nerve cell and in the 

 dermal chromatophore is sufficiently obvious, especially within 

 the nucleus of the former. The evidence for the nerve cell corrob- 

 orates Hertwig's idea ('02), which Schultz likewise follows in 

 his deductions, that the function of the nucleolar substance is the 

 synthesis of chromatin by uniting to itself substances derived 

 from the cytoplasm. When therefore the chromatin within the 

 nucleolus or preferably karyosome of the nerve cell is used up or 

 breaks down, as occurs respectively in exhaustion and in depression 

 (karyolysis and karyorrhexis) the basic stain gives way to the 

 acid stain of the nucleolar substance — the true nucleolar remnant 

 of that amphinucleolus. Consequently, the browning of this 

 nucleolus, which was noted in the description of chronic depression, 

 follows exactly the sequence of the chromatophore. The chro- 

 matin breaks down to nucleolar substance and this is trans- 

 formed into pigment. More simply, the direct transformation 

 of the nucleolar substance outside of the karyosome is shown 

 by its replacement by pigment granules. 



