EFFECTS OF FORMALDEHYDE ON BRAIN OF RAT 



297 



for the dilution of the solution by the tissue fluids is greater when 

 a small amount of solution is used, and the effect is then the 

 same as if the brains were kept in a weaker solution. According 

 to the observations of Hrdlicka, the weight increase in brains 

 treated with unneutralized solutions of formaldehyde is "larger 

 with the weakest solutions and decreases as the proportion of 

 formalin increases." It is evident, therefore, that in these exper- 

 iments some factor, possibly the NaCOs used in neutralizing the 

 solutions, has checked the swelling action of the weakened solu- 



TABLE 6 



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

 neutralized solution of 4 psr cent formaldehyde made fresh for each lot of animals 

 killed {averages for two brains at each age) 



1 Maximum weight increase. 



tion. This seems probable from the results obtained in the second 

 set of experiments in this series which show that a weak acid 

 solution of formaldehyde causes a greater amount of swelling 

 than does a stronger one. 



The final weight changes for the various groups of brains are 

 plotted in the graphs in chart 6. 



Table 7 gives the data obtained in the experiments in which 

 brains of different ages remained for four weeks in 20 cc. of a 

 non-neutralized solution of 4 per cent formaldehyde. 



In this instance brains of new-born rats do not show such 

 striking weight changes as are shown in table 5. The initial rise 



