EFFECTS OF FORMALDEHYDE ON BRAIN OF RAT 



301 



TABLE 8 



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

 neutralized solution of 4 per cent formaldehyde kept at a constant temperature of 

 S6°C. {averages for two brains at each age) 



1 Maximum weight increase. 



with Donaldson's ('94) observations that brains of sheep kept in 

 a 2 per cent solution of bichromate of potassium at a tempera- 

 ture of 38°C. attain their maximum weight at a very early period 

 and gain relatively less than when kept at a temperature of 10 

 to 17°C. In the case of the rats' brains kept at a temperature 

 of 36°C. the decrease in the amount of swelUng can be attributed, 

 in part at least, to the fact that this temperature partially de- 

 composes the solution of formaldehyde and liberates a consider- 

 able amount of formaldehyde gas. This of course weakens the 

 solution, and a weaker solution of formaldehyde that has been 

 neutralized with NaCOa does not cause as much swelling in rats' 

 brains as does a stronger one, as was shown in the experiments 

 in Series 4. 



Graphs for the weight changes in the various sets of brains 

 kept at a temperature of 36°C. are shown in chart 8. All of 

 these graphs, it may be noted, are grouped in pairs according 

 to the age of the animals. While a paired arrangement of some 

 of the graphs is to be found in other charts (6, 7 and 9), in no 

 case is the phenomenon as marked as in chart 8. 



