NERVOUS SYSTEM 



113 



of solids in brains that have been subjected to the action of such a 

 solution is always less than that found in the fresh brains of animals of 

 the same age. Brains of very young rats lose much more of their solids 

 than do brains of older animals. 



TABLE 75 

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

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

 killed (averages for two brains at each age) 



TIME SOLUTION' ACTED 



1 day. . . 

 3 days. . 

 7 days. . 



2 weeks 



3 weeks 



4 weeks 



AGE OF RATS 



New- 

 born 



60.4 



65.8^ 



65.4 



65.1 



64.8 



61.7 



10 

 days 



54.7 



58.5* 



58.5 



58.4 



58.2 



57.8 



Average percentage gain.. 63.4 57.7 49.2 45.9 46.4 44.8 40.3 35.8 



20 

 days 



45.8 

 52.9^ 

 48.3 

 48.9 

 48.9 

 50.4 



40 

 days 



47.6^ 

 47.4 

 45.6 

 45.3 

 44.7 

 45.1 



50 

 days 



50.4^ 



47.7 

 45.1 

 44.8 

 45.2 

 45.4 



70 

 days 



44.9 

 48.8* 

 44.2 

 43.2 

 43.9 

 44.9 



100 

 days 



44.2* 

 42.7 

 38.3 

 38.6 

 38.8 

 39.3 



200 

 days 



36.1 



40.1" 



36.2 



33.0 



34.7 



34.9 



Maximum weight increase. 



TABLE 76 

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

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

 animals killed (averages for two brains at each age) 



TIME SOLUTION' .^CTED 



1 day... 

 3 days . . 

 7 days . . 



2 weeks 



3 weeks 



4 weeks 



AGE OF RATS 



New- 

 born 



34.5^ 



18.6 



9.9 



3.5 



0.4 



-1.5 



10 

 days 



37.3 



45.1^ 



37.8 



30.4 



25.9 



23.5 



Average percentage gain.. 13.1 33.3 35.6 33.5 36.0 34.1 32.5 28.9 



20 



days 



36.7 



45.4* 



38.2 



34.6 



30.7 



27.9 



40 

 days 



39.7^ 



39.1 



35.6 



31.5 



28.3 



26.6 



50 

 days 



44.2^ 



42.8 



38.1 



32.6 



30.6 



27.8 



70 

 days 



39.5 

 42.3* 

 34.3 

 31.5 

 29.5 

 27.3 



100 

 days 



41. r 



39.4 

 33.8 

 29.0 

 27.4 

 24.3 



200 

 days 



32.2 



35.4* 



30.2 



26.7 



24.5 



24.5 



* Maximum weight increase. 



10. Brains of animals infected with pneumonia show a slightly 

 greater percentage weight increase when treated with a 4 per cent 

 solution of formaldehyde than for the brains of healthy animals. 



11. Even under the most favorable conditions an aqueous solution 

 of formaldehyde is not a satisfactory fixative for the cell structures in 



