EFFECTS OF FORMALDEHYDE ON BRAIN OF RAT 



287 



a gradual decrease in weight until, after the brains have been in 

 the solution for eighteen weeks, the percentage weight increase 

 is reduced from 5 to 15 per cent below the maximum. In general, 

 as shown in table 1, the amount of swelling seems to increase 

 with the age of the rat up to the forty-day period, then it 

 decreases slowly. Under the conditions of the experiments, 

 therefore, the amount of swelling is not directly proportional 

 either to the age of the animal or to the size of the brain. 



Chart 1 shows the graph for the final percentage weight in- 

 crease in the A^arious sets of brains at the end of eighteen weeks. 



Percentage weight increase. 



Age in days. 



2 00 



Chart 1 Showing the final percentage weight increase in a series of rats' 

 brains kept for eighteen weeks in stock solutions of 4 per cent formaldehyde. 



Starting relatively low the graph reaches its highest point with 

 the forty-day group. Then comes a decided drop at fifty days, 

 followed by a sharp rise at seventy days and a slight falling at 

 the adult stage. As all the brains were kept in the same amount 

 of solution under similar conditions of light and of temperature, 

 the fall in the graph at the fifty-day period seems explicable 

 only on the assumption that the stock solution of formaldehyde 

 used in this instance had undergone some chemical change which 

 had lessened its swelling action on the brain tissue. 



As the stock solutions of 4 per cent fomialdehyde used in this 

 series of experiments had been kept in the laboratory for var}'- 



