W. Koch and M. L. Koch 427 



out the nervous system. Neurokeratin occurs in the medullated sheath 

 of the nerve fiber. The other proteins occur in the axon of the nerve fiber 

 as well as in the cell body and its dendrites. 



Physiological significance. The proteins have usually been considered 

 as the essentially living part of the protoplasm, but some of them, like 

 neurokeratin, are undoubtedly inactive and represent supporting struc- 

 tures. The same may be said of the proteins which make up the fibers 

 of the glia cells. It is therefore impossible to tell at the present time to 

 just what extent and in what proportion the proteins are involved in the 

 chemical activities of the nervous system. The significance of the neutral 

 sulphur compounds, which represent simpler cleavage products of the 

 larger protein aggregates, will be discussed later as having an important 

 bearing on this point (see p. 431). 



Phosphatides. 



Chemistry. These represent complex combinations of fatty acids, phos- 

 phoric acid, glycerin, and nitrogen complexes of the nature of choline, 

 and include among other things lecithin and kephalin. The chemistry of 

 this group is very much in need of revision, as some of its members are 

 not so simple as the older work of Hoppe-Seyler has led us to infer. The 

 group does not include lecithin in combination with sulphur or cerebrin. 

 The phosphatides as here given are calculated from the phosphorus of 

 the lipoid fraction on the assumption that they have an average molecular 

 weight of 800. Correction must be made for the phosphorus of the 

 sulphatides. 4 



Anatomical distribution. Comparison of cortex and corpus callosum 5 in- 

 dicates that the phosphatides are not very differently distributed between cell 

 body and nerve fiber. Analyses of the brain at a period when medullation 

 has not begun, but when the cell processes are growing freely, indicate 

 that the phosphatides are largely associated with the axon. If mitochon- 

 dria consist largely of phosphatides, as has been suggested, the observa- 

 tions of Cowdry would give us a picture of their distribution in the cell 

 body. The absence of mitochondria in the axon, which is known to con- 

 tain phosphatides, would not argue against this, as there is some evidence 

 that the phosphatides of the processes and the cell body are different in 

 their behavior. 



Physiological significance. The phosphatides, like the proteins, may be 

 considered to be intimately associated with the vital processes of the living 

 protoplasm. Their colloidal nature and relation to inorganic ions, as well 



4 Calculations for phosphatides. The total lipoid phosphorus found times 

 25.77 gives the phosphatides, on the basis that 3.88 per cent of the phospha- 

 tides consist of phosphorus. Since 51.2 per cent of the sulphatides are phos- 

 phatides, that amount was deducted from the total phosphatides found. 

 The difference was considered as free phosphatides. 



5 Koch, W.: Amer. Journ. of Physiol, xi, pp. 326-328, 1904. 



