EFFECTS OF FORMALDEHYDE ON BRAIN OF RAT 



303 



TABLE 9 



Percentage weight increase in rats' brains, each left for four iveeks in 40 cc. of a 

 neutralized solution of 4 per cent formaldehyde kept at a temperature of 8 to 11°C. 

 {averages for two brains at each age) 



1 Maximum weight increase. 



This latter result is what might be expected, since a low tem- 

 perature tends to lessen the amount of absorption of a liquid 

 by brain tissue. This is the only set of experiments in which 

 the average gain in the brains of adult rats is greater than that 

 in the brains of 100-day-old animals. The increase, however, 

 amounts to only about 1 per cent, so it is probably merely a 

 chance variation. 



Chart 9 shows the graphs plotted for the weight changes in 

 the brains kept at a low temperature. There is a tendency here 

 also to a paired arrangement of the graphs according to age, 

 but it is not as pronounced as in chart 8. 



The final percentage gain in weight for the two sets of brains 

 used in this series of experiments is shown b}^ graphs in chart 

 10. The form of the graphs is much the same, but the graph 

 for the brains kept at relatively high temperature {A ) runs some- 

 what higher than that for the brains kept at a low temperature 

 (B). A difference of 25°C. in the temperature of the solutions 

 in which the brains are kept has but comparatively little effect 

 on the final weight increase at the end of four weeks 



