312 HELEN DEAN KING 



SUMMARY 



1. A 4 per cent solution of formaldehyde causes a pronounced 

 swelling in the brains of rats of all ages. 



2. A solution of formaldehyde undergoes some chemical change 

 on standing, since a solution five months old causes less swelling 

 in the brain of the rat than does a freshly made solution. 



3. A 4 per cent solution of formaldehyde neutralized with 

 NaCOs 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 neutralized 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 36°C., 

 they undergo a greater amount of swelling than is produced 

 when the solution is kept at a temperature of 8 to 11°C. The 

 maximum weight increase in the brains is reached by the end 

 of the first day in the fonner 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 maxi- 

 mum earlier than do those of older animals. 



7. The percentage weight increase in rats' brains as the result 

 of the action of a 4 per cent formaldehyde solution tends to be 

 greater in the brains of young animals than in those of adults. 



8. In animals of the same age the larger brain does not show 

 a greater percentage weight increase after treatment with a solu- 

 tion of formaldehyde than does the smaller one. 



