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 for 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) 



* 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 per cent formaldehyde made fresh for each lot of 

 animals killed (averages for two brains at each age) 



AGE OF RATS 



* 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 



