CHEMICAL CHANGES IN HUMAN BRAIN 447 



brains. This cannot be an analytical error, because the same 

 amount was obtained in two analyses made at different times in 

 the series. 



The brain marked '8-24 mo.' was labeled '2 years' when sent 

 for analysis. There seems to be no good reason for questioning 

 the accuracy of this information. However, the weight of the 

 brain indicates an infant of a few months. Its water content 

 suggests an infant of about eight months, while some of the phos- 

 phatids would favor a slightly greater age, as would the weight 

 of cerebellum and stem. Very likely this brain was two years 

 old, but subnormal. In spite of the uncertainty concerning the 

 brain, it is included in this series because it was the only one of 

 this age available, but it is considered with the greatest reser- 

 vation in forming general conclusions. 



No brains about five and twelve years of age could be 

 obtained. This leaves the series incomplete. 



Unfortunately, it was not known until the investigation was 

 nearly finished that the method used for sulphur determination 

 gave low results. This vitiates to a certain extent the reports 

 on the various forms of sulphur, the sulphatids, and because of 

 the methods of calculating the data, the cerebrosides, and the 

 undetermined cholesterol. It was planned to make direct cho- 

 lesterol estimations, but the series took so much longer than ex- 

 pected that these estimations were omitted. 



Analyses 7 and 10 were made together. A combination of 

 circumstances tendered their phosphatid determinations some- 

 what unreliable. If the solutions to be precipitated by chloro- 

 form and hydrochloric acid become too warm and are allowed to 

 stand too long, the phosphatids are incompletely precipitated. 

 This gives not only an error in phosphatids, but, by difference, 

 in 'cholesterol, etc' and in extractives. 



Many ways were found of improving the method after be- 

 ginning this series, but they could not be adopted because of the 

 effect on comparisons of results. One always sees many ways of 

 improving an investigation after it is finished, and that is un- 

 usually true of this investigation. 



