EFFECTS OF FORMALDEHYDE ON BRAIN OF RAT 



293 



than those of the new-born: those belonging to the 20, 40, 50 

 and 70-day groups swell nearly the same amount, showing a maxi- 

 mum weight increase of from 49 to 53 per cent. In older animals 

 the maximum increase in weight is somewhat less, amounting to 

 44 per cent in the case of 100-day animals and 40 per cent in 

 the adults. The weight changes for each set of brains during 

 the four weeks the experiments were continued are shown in the 

 series of graphs in chart 3. 



Age of rat. 

 New born. 



Time in days. 



40 days. 

 50 days. 

 ^70 days. 

 ^100 days. 

 200 days. 



2B 



Chart 3 Showing the weight changes in brains of rats of various ages, each 

 kept for four weeks in 40 cc. of a 4 per cent solution of formaldehyde neutralized 

 with NaCOa. 



As presumably all the solutions used in this set of experiments 

 had the same chemical composition, the variations in the amount 

 of swelling in the different groups of brains can doubtless be 

 attributed to a difference in the chemical composition of the 

 brains at different ages. The size of the brain, as will be shown 

 later, is not a factor that influences the amount of swelling to 

 any considerable extent. 



