W. Koch and M. L. Koch 447 



teins are present in the brain in nearly equal proportions. For 

 the sake of comparison, the corresponding values for the spinal 

 cord at 120 days have been introduced into this chart. 



To make easier the comparison between the relations of pro- 

 teins and lipoids in the brain and in the spinal cord, it is assumed 

 for the purposes of the chart that the dry weight of the cord is 

 the same as that of the brain at 120 days. Since the cord con- 

 tains a larger proportion of white matter than does the brain, 

 we find that the lipoids in this case predominate over the proteins. 

 This indicates that the chemical differentiation during the growth 

 of the nervous system, as recorded in this paper, is largely con- 

 cerned with the development of the medullated nerve fiber. 



Chart 4 shows very strikingly the great decrease with advanc- 

 ing age in the non-colloidal contrasted with the corresponding 

 increase in the colloidal sulphur and phosphorus compounds. 

 Particular attention is called to the neutral sulphur which in the 

 young, rapidly metabolizing tissue constitutes the greater propor- 

 tion of the total sulphur, whereas it becomes extremely small at 

 210 days when growth metabolism is at an end. Evidently this 

 fraction may, with reserve, be considered an index of growth 

 metabolism. With advancing age the colloidal, less active, sub- 

 stances gradually crowd out the non-colloidal. This is in strik- 

 ing accord with the interesting suggestions of Child 33 that senes- 

 cence is due to the accumulation of these colloidal solids, which 

 interpose resistance to metabolism. 



Finally we find the growth process characterized by a steady 

 diminution in the proportions of water and an increase in the pro- 

 portion of solids. This change is due not alone to medullation in 

 the strict sense, since as Donaldson 34 has pointed out the decrease 

 begins before medullation, between birth and ten days in the rat. 

 He attributes it to a rapid growth of the axone at this time. Water 

 and the proportion of neutral sulphur are therefore criteria of the 

 youthfulness of tissue, while the increase of lipoid sulphur (sul- 

 phatides) is a criterion of medullation. 



33 Child, C. M. : Archiv. f. Entwicklungs-mechanik d. Organismen, xxxi, 

 p. 571, 1911. 



34 Donaldson, H. H. : Journ, of Neurology and Psychology, xx, p. 138, 

 1910. 



