274 Chemical Differentiation of the Brain 



Cholesterol. The figures for cholesterol were not determined by 

 me, but were taken from Mendel 9 and incorporated here for the 

 sake of completeness. 



This leaves undetermined from 2 to 3 per cent which is not more 

 than would be expected in the errors involved in making so many 

 determinations from one tissue and calculating approximate con- 

 stituents from assumed factors. 



The distribution of sulphur in per cent of total sulphur is widely 

 different in the two forms, but as this is not correlated with age 

 but is apparently a species peculiarity, the results are not out of 

 harmony with the foregoing conclusions. 



The distribution of phosphorus between the protein, lipoidand 

 water-soluble phosphorus is closely similar in the rat and the 

 50 and 100 mm. pig fetus, showing the physiological ages to corres- 

 pond. 



The remarkably high figure for neutral and inorganic sulphur in 

 the rat at birth requires an explanation but it is not possible to 

 give this with the data so far at hand. 



The general conclusions from these figures are, that from a 

 chemical standpoint the brain of the new born rat is about as imma- 

 ture as that of the 100 mm. pig fetus, being on the whole a little 

 less differentiated than the latter. 



The differences between the brain of the 50 mm. and the 100 

 mm. pig fetus are not marked, and this would indicate that there oc- 

 curs between these ages an increase in weight unaccompanied by any 

 significant change in chemical composition. This would corres- 

 pond with the results of Mendel 10 and Raske 11 who found that in 

 the brains from these young fetuses there is no chemical dis- 

 tinction between grey and white matter. Moreover the brain 

 of the 50 mm. pig fetus is the youngest which it is practicable to 

 obtain for analysis and even at this age the tissues are so watery 

 and filled with lymph that some error is thereby introduced in the 

 analysis of the constituent tissues. 



Since the brain of the 50 mm. pig fetus shows no material differ- 

 ences from that of the 100 mm. pig fetus and the latter is no more 



9 L. B. Mendel and Charles S. Leavenworth : Chemical Studies on Growth. 

 IX. Notes on the Composition of Embryonic Muscular and Nervous Tissues. 

 Amer. Journ. of PhysioL, xxi, p. 103, 1908. 



10 Ibid. 



11 Raske: Zeitschr.f. physiol. Chem., x, p. 340, 1886. 



