EFFECTS OF FORMALDEHYDE ON BRAIN OF RAT 285 



THE WEIGHT CHANGES PRODUCED BY FORMALDEHYDE IN BRAINS 

 OF ALBINO RATS OF KNOWN AGES 



Series 1. This was a preliminary set of experiments made to 

 discover the general effects of a 4 per cent solution of formalde- 

 hyde on the brains of rats of different ages. In these experi- 

 ments brains were taken from animals of the following ages : new- 

 born, 10, 20, 40, 50, 70 days and adults, approximately 200 days 

 old. Three rats of each age were used, animals of a given age 

 being taken from the same litter except in the case of adult rats 

 which were of unknown parentage and therefore may or may 

 not have belonged to the same litter. As it w^as not possible 

 to obtain all the rats wanted for the experiments at one time, 

 the initial weighing of the first lot of brains was made early in 

 October, 1910, while the final lot of material was not obtained 

 until February, 1911. Each brain w^as put into 40 cc. of a 4 per 

 cent solution of formaldehyde that was neutraUzed with NaCOs. 

 The solution of formaldehyde used was, in some cases, one that 

 had been made up for some weeks; in other cases a fresh solution 

 was made as wanted, either from formalin that had been in the 

 laboratory for some time or from a newly purchased supply. 

 The age of the solution or the condition of the formalin used in 

 making the solution were factors that were not thought to be 

 of importance and therefore no attention was paid to them. 



The different lots of brains were weighed at irregular intervals 

 during the first week they were in the solution, then every seven 

 days for nine weeks. At the end of this time each brain was 

 transferred into a fresh solution, made at the time it was wanted 

 for use. The bottles containing the brains were then sealed with 

 paraffine and kept for two months at laboratory temperature. 

 After eighteen weeks the brains received their final weighing and 

 they were then dried to obtain the percentage of solids. In 

 each set of brains of the same age the individual weighings were 

 very uniform, as they showed a difference of only 2 or 3 per 

 cent in the majority of cases. These differences can undoubtedly 

 be ascribed to the fact that animals taken from the same litter 

 often vary considerably in size even when they are of the same 



