112 



ANATOMY 



7. The percentage weight increase in rats' brains as the result of 

 the action of a 4 per cent formaldehyde solution tends to be greater 

 in the brains of young animals than in those of adults. 



TABLE 73 

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

 neutralized solution of 4. per cent formaldehyde made Jive months before the experi- 

 ments began (averages for three brains at each age) 



* Maximum weight increase. 



TABLE 74 

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

 neutralized solution of 4 per cent formaldehyde made at the time the experiments 

 began (averages for three brains at each age) 



TIME SOLUTION ACTED 



1 day... 

 3 days . . 

 7 days. . 



2 weeks 



3 weeks 



4 weeks 

 10 weeks 



AGE OF BATS 



New- 

 born 



44.4^ 



42.0 



41.5 



38.0 



37.7 



36.1 



33 9 



10 



days 



58.2 



64.6^ 



62.1 



62.9 



63.4 



62.8 



61.4 



Average percentage gain.. 39.1 62.2 40.0 36.4 36.7 35.4 41.3 31.9 



20 



days 



39.5 



41.5* 



40.1 



39.7 



40.0 



39.9 



39 4 



40 50 



days days 



37.9=' 

 37.6 

 36.4 

 35.9 

 35.7 

 35.5 

 35.5 



39.3^ 



38.5 



35.6 



36.1 



36.9 



35.4 



36.1 



70 

 days 



34.4 



38.6* 



34.1 



34.9 



34.3 



35.7 



35.5 



100 



days 



45.6* 



43.1 



41.1 



41.0 



40.4 



40.5 



37.7 



200 

 days 



32.4 



34.7" 



30.9 



30.8 



31.2 



31.6 



31.8 



* Maximum weight increase. 



8. In animals of the same age the larger brain does not show a greater 

 percentage weight increase after treatment with a solution of formal- 

 dehyde than does the smaller one. 



9. A 4 per cent solution of formaldehyde extracts solids from the 

 brains of rats of all ages. This is shown by the fact that the percentage 



