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HELEN DEAN KING 



The data obtained when brains were kept in a non-neutralized 

 solution of 4 per cent formaldehyde for four weeks are given in 

 table 5. 



TABLE 5 



Percentage weight increase in rats' brains, each kept for four weeks in 40 cc. of a 

 non-neutralized solution of 4 per cent formaldehyde made fresh for each lot of 

 animals killed {averages for two brains at each age) 



1 Maximum weight increase. 



As shown in the table, the effects of an acid solution of fonn- 

 aldehyde on the brain of a new-born rat is most remarkable. 

 The maximum weight increase amounts to only 34.5 per cent of 

 the original brain weight, and it is attained at the end of the 

 first day. There is then a rapid decrease in weight with each 

 succeeding weighing until, at the -end of four weeks, the brain 

 actually weighs 1.5 per cent less than the original weight: this 

 indicates that the solution has extracted some substance from 

 the brain tissue. In both the brains of this age used the per- 

 centage weight changes were practically the same, as there was a 

 difference between them of less than 2 per cent at any weighing. 



Brains of ten-day-old rats do not show such remarkable weight 

 changes as do those of new-born animals. In fact, an acid solu- 

 tion of 4 per cent formaldehyde causes nearly the same amount 

 of swelling in brains of all ages from ten days to maturity, there 

 being a difference of less than 10 per cent between the maximum 

 weight increase in any two sets of brains, and a difference of 



