EFFECTS OF FORMALDEHYDE ON BRAIN OF RAT 



299 



TABLE 7 



Percentage weight increase in rats' brains, each kept for four weeks in 20 cc. of a 

 non-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. 



of 38.9 per cent, found at the end of the first day, is greater by 

 4 per, cent than that found in the previous set of experiments, 

 but the subsequent fall in weight is not so rapid and at the end 

 of four weeks the brains still weigh an average of 13.4 per cent 

 above the original weight and therefore do not appear to have 

 lost any of their substance. In these experiments the greatest 

 percentage gain in weight occurs in the brains of the ten-day 

 and twenty-day-old animals, the average gain for the entire 

 period over which the weighings extended being in each case 

 more than 40 per cent of the fresh weight: the data for the 

 brains of animals from 40 to 200 days old differ but slightly from 

 the corresponding data in table 5. The weight changes in the 

 groups of brains of different ages are plotted in chart 7. 



The contrast between the results of this series of experiments 

 and those of Series 3 is brought out sharply in chart 5. Graph 

 C was plotted from the final weights of the brains kept in 20 cc. 

 of a neutralized solution of 4 per cent formaldehyde; graph D 

 was plotted from data obtained where 20 cc. of a non-neutralized 

 solution was used. These graphs run, for the most part, between 

 the graphs A and B, which were plotted from the final brain 



