302 



HELEN DEAN KING 



Age of rat. 



New bom., , 

 60 



10 days.. , 



40 days^ 

 20 days. 50 

 50 days.. , 

 70 days. 

 100 days., 

 200 days^ , 

 30 



I Percentage weight increase. 



40 



Time in days. 



L 



Age of rat 

 to days. 

 ,20 days. 

 ,40 days. 

 •New bom. 

 ■70 days. 

 ~50 days. 

 100 days, 

 -200 days. 



Chart 8 Showing the weight changes in brains of rats of various ages, each 

 remaining for four weeks in 40 cc. of a neutralized solution of 4 per cent formalde- 

 hyde kept at a constant temperature of 36°C. 



Table 9 gives the data for the weight changes in the brains 

 kept in 4 per cent formaldehyde for four weeks at a temperature 



of 8 to irc. 



As indicated in table 9, the maximum weight increase in all 

 sets of brains was attained on the third day except in the case 

 of the brains of the new-born rats where, as in most of the pre- 

 vious experiments, the maximum increase comes at the end of 

 the first day. The subsequent loss in weight is very slight and 

 it does not amount in any case to more than 8 per cent of the 

 original brain weight. While the brains of young rats (birth to 

 40 days) show a relatively greater weight increase than the brains 

 of older animals, there is not the very uniform decrease with 

 advancing age that was noted in the previous set of experiments 

 (table 4) where the brains were kept in 40 cc. of a neutralized 

 solution at ordinary room temperature (about 20°C.), neither is 

 the average increase for the various groups of brains as high. 



