290 



HELEN DEAN KING 



solution causes less swelling in every case than the one that was 

 comparatively fresh when used, the difference between the aver- 

 age percentage weight increase in the various sets of brains of 

 like ages ranging from 10 to 31 per cent. 



The final percentage weight increase in each set of brains at 

 the end of ten weeks is shown graphicalh^ in chart 2. The gen- 

 eral form of the graphs is much the same, yet the graph for the 



Chart 2 Showing the final percentage weight increase in two series of rats' 

 brains, each kept for ten weeks in a neutralized solution of 4 per cent formalde- 

 hyde. A, solution made when the experiments began; B, solution five months 

 old when used. 



brains kept in the old solution (B) is much lower at every point 

 than that for the brains kept in the freshly made solution (A). 

 The marked difference in the effects of these two solutions is 

 not due to the fact that the older solution had become acid by 

 standing while the newer solution had remained neutral. Both 

 solutions were tested with good litmus paper on December 15, 

 1911, and each was found to give a very slight alkaline reaction. 

 Since solutions of formaldehyde are readih' decomposed it is prob- 



