NERVOUS SYSTEM 



111 



TABLE 72 Concluded 



3. A 4 per cent solution of formaldehyde neutralized with 

 produces a much greater amount of swelling in the brain of the rat 

 than does a solution that has a faintly acid reaction. 



4. A strong neutralized solution of formaldehyde causes a greater 

 percentage weight increase in the rat's brain than does a weak neutral- 

 ized solution. A reverse result is obtained when the solutions are not 

 neutralized. 



5. If rats' brains are subjected to the action of a solution of 

 formaldehyde that is kept at a constant temperature of 36C., they 

 undergo a greater amount of swelling than is produced when the solution 

 is kept at a temperature of 8 to 11C. The maximum weight increase 

 in the brains is reached by the end of the first day in the former case, 

 and not until the third day in the latter case. 



6. When the conditions under which the solution acts are uni- 

 form, the maximum weight increase in rats' brains subjected to the 

 action of a 4 per cent solution of formaldehyde is attained in all cases 

 by the third day, and there is then a gradual decrease in weight. Brains 

 of very young animals tend to reach the maximum earlier than do those 

 of older animals. 



