EFFECTS OF FORMALDEHYDE ON BRAIN OF RAT 291 



able that the older solution underwent some chemical change 

 through standing. There was, however, no evidence of the for- 

 mation of paraformaldehyde when the bottle containing the old 

 solution was first opened; the liquid appeared perfectly clear and 

 had the characteristic odor of formaldehyde. No analysis of the 

 solution was made, so it is not possible to state just what changes 

 had occurred in it. ■ 



The results of this series of experiments indicate unmistakably 

 that the age of the animal is an important factor in determining 

 the amount of swelling that the brain will undergo in 4 per cent 

 formaldehyde. In general, the younger brains absorb a rela- 

 tively greater amount of liquid than do the older ones. This 

 result, which accords with the observations of Hrdlicka and of 

 Donaldson ('94), can doubtless be ascribed, in part at least, to 

 the fact that the brains of young rats contain normally a greater 

 percentage of water than do the older ones (Donaldson '10). 

 According to the observations of Watson ('03) meduUation in 

 the rat's brain does not begin until the eleventh day after birth. 

 The non-medullation of the fibers and the deficiency in support- 

 ing tissue are also factors that in all probability tend to increase 

 the amount of swelling in the young brains. 



Series 3. These experiments were made to ascertain whether 

 the amount of swelling in the brain placed in 4 per cent formal- 

 dehyde will be influenced by the neutrahzation or by the non- 

 neutralization of the solution. Lee ('05) does not approve of the 

 neutralization of formaldehyde solutions, and he states that the 

 slightly acid reaction that is usually found ''is, as a rule, an 

 advantage;" Bayon ('05), on the other hand, believes that an 

 acid solution of formaldehyde is injurious to nerve tissue, and 

 he advises that all such solutions should be neutralized with 

 NaCOa. In carrying out these experiments it was considered 

 necessary that the age of the solution should not be a factor 

 that could influence the results, and, therefore, a fresh solution 

 was made from a common stock supply of formalin when each 

 lot of animals was killed. The four rats of each age that were 

 used were taken from the same litter. Two brains from each 

 group were put into 40 cc. of a solution neutralized with NaCO^; 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 23, NO. 4 



