432 Chemical Differentiation of the Brain 



non-colloidal, relatively smaller, neutral sulphur molecules is at a maxi- 

 mum. This is what we should expect when we consider living matter 

 not as a collection of highly organized molecules, but rather as a hetero- 

 geneous substratum in which relatively smaller molecules or their dissoci- 

 ated products are engaged in chemical transformations. As the tissues 

 grow and become more highly differentiated and mature, more and more 

 protein is laid down as structural material, and the proportion is shifted . 

 in the direction of the protein sulphur. A comparison of the cortex of 

 the human at two years and at maturity illustrates this point. 16 



2 years' cortex Protein S, 63; Neutral S, 22. 



19 years' cortex Protein S, 73; Neutral S, 12. 



The change suggests, therefore, a decrease in chemically active mate- 

 rial associated with the increasing complexity of the tissue. Such data 

 as we have at hand indicate that we have in the protein sulphur and neu- 

 tral sulphur ratio a valuable means of measuring the relative growth 

 intensity of the nervous system at different periods during its development 

 after the state of cell division has practically ceased. 



There might be another way of measuring this intensity of chemical 

 activity, namely, by means of the inorganic^ sulphates, which represent 

 the end products and the final state of oxidation of the compounds involved 

 in these reactions, but they are eliminated rather easily from the cell, and 

 it is therefore difficult to attach any significance to their variations. 



Distribution of phosphorus. 



Chemistry. PROTEIN P. This group represents phosphorus largely in 

 combination as nucleic acid. In the nervous system this nucleic acid is 

 combined with such a very large amount of protein 17 that the per cent of 

 phosphorus in the resulting nucleoprotein drops to 0.57 per cent as com- 

 pared with 3 to 4 per cent in such a tissue as the pancreas. 



LIPOID P. Already discussed under phosphatides. 



WATER-SOLUBLE P. This group includes non-colloidal, water-soluble 

 organic combinations of phosphoric acid and inorganic phosphates. On 

 account of the relative ease with which the organic extractive combina- 

 tions of this form of phosphoric acid break down, it is difficult to estimate 

 the proportion which is in organic combination. The results which are so 

 far recorded represent, therefore, rather the possible maximum, than a 

 very close approach to the actual value. (See articles of Grindley, 18 Trow- 

 bridge, 19 and Forbes. 20 ) 



16 Koch, W. and Mann, S. A.: Journ. of PhysioL, xxxvi, p. 2, 1907. 



17 Also accounts for poor staining reaction of neurone nucleus. 



18 Grindley: Journ. of Amer. Chem. Soc., xxviii, pp. 25-63, 1906. 



19 Trowbridge, P. F. and Francis, C. K.: This Journal, vii, pp. 481-501, 

 1910. 



20 Forbes, E. B. : Ohio Agric. Exp. Sta. Bulletin 215, 1910, pp. 459-489. 



