THE PHYSIOLOGICAL CHEMISTRY OF THE NEURON. 555 



phologically, exactly as the stainabk substance in nerve-cells. 

 He described them in gland-cells, liver-cells, in cells of the 

 pancreas, in the cells of some sarcomatous tumors, in certain 

 connective-tissue cells, but especially in normal and pathological 

 lymph-glands. Cajal 44 also asserts that the stainable substance 

 of Nissl is not specific for the nerve-cells, as he has demon- 

 strated its presence in certain of the leucocytes and of the con- 

 nective-tissue elements." Nissl's bodies appear to us, therefore, 

 as constituting an organized component of the ground-sub- 

 stance of the neuron, a nucleo-albumin rich in phosphorus, 

 which, judging from its similarity to a large number of cellular 

 structures elsewhere in the organism, represents the cell-struct- 

 ure itself, precisely as is the hepatic cell when free from glyco- 

 gen, bile, or the agencies from which these are derived. It is 

 to the neuron what the neurilemma, Mauthner's sheath, etc., 

 are to the internodal segment of a nerve, and includes as 

 does the protoplasmic membrane of Schwann the nucleolated 

 nucleus. 



The unstainable portion must be the equivalent of myelin: 

 the white substance of Schwann. We have seen that this is 

 also unstainable. Even picrocarmine does not stain it, and 

 Eanvier states that the axis-cylinder becomes stained at the 

 nodes because there is no myelin in this region of the nerve. 

 The similarity between myelin of the nerves and that of the 

 cerebro-spinal system is emphasized by Foster when he says: 

 "Obviously the fat of the white matter of the central nervous 

 system and of spinal nerves (of which fat by far the greater part 

 must exist in the medulla, and for nearly the whole of the 

 medulla) is a very complex body indeed, especially so if the 

 cholesterin exists in combination with the lecithin, or cerebrin 

 (or protagon). Being so complex, it is naturally very unstable, 

 and, indeed, in its stability resembles proteid matter." This 

 also suggests, however, that protagon, a nitrogenous body con- 

 taining phosphorus isolated by Liebreich from brain-substance, 

 may be the unstainable substance we are seeking. Hoppe-Sey- 

 ler and Diakonoff, having found it to be composed of lecithin 

 and cerebrin, the direct connection with the former is not re- 



** Cajal: Revista trimest. micrografica, vol. i, No. 1, March, 1896. 



