EFFECTS OF FORMALDEHYDE ON BRAIN OF RAT 305 



THE EFFECTS OF 4 PER CENT FORMALDEHYDE ON THE PERCENT- 

 AGE OF SOLIDS IN THE BRAIN OF THE ALBINO RAT 



All the brains used in the above series of experiments, with 

 the few exceptions that will be noted later, were heat dried for 

 one week at the end of the weighing period to obtain the amount 

 of dry substance. The percentage of solids left in the brains 

 after treatment with the formaldehyde solutions was then cal- 

 culated from the weight of the brains when fresh. A summary 

 of the results obtained for the brains of each age is given in 

 table 10. This table shows also the normal percentage of solids 

 in the brains of rats of various ages as deduced from data given 

 by Donaldson ('10) in his paper, ''On the percentage of water 

 in the brain and in the spinal cord of the albino rat." 



As shown in this table, the normal percentage of solids in the 

 brain of the rat, as deduced from Donaldson's data, varies directly 

 with the age of the animal, being 12.2 per cent of the total brain 

 weight in new-born rats and 21.6 per cent in the brains of adults. 

 The computations made for the brains used in these various 

 series of experiments show that in every case the percentage of 

 solids is less than that normally found in fresh brains at the 

 age observed, and that it increases from birth to maturity in a 

 regularly striking manner. It follows from this that formalde- 

 hyde solutions extract some of the solids from the brain tissues. 

 Brains of new-born rats suffer the greatest loss of solids; brains 

 of adults are least affected. 



The amount of solids lost from the brain of the rat through 

 the action of a formaldehyde solution is not directly correlated 

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

 Brains of very young animals (birth to 10 days) lose about 30 

 per cent of their solids after treatment with a solution of formal- 

 dehyde. The average loss from the brains of older animals falls 

 from 7.4 per cent in the 20-day-old brains to 1.5 per cent in the 

 brains of animals 40 days of age. In brains of 50-day-old rats 

 there is an increase in the extraction of solids by formaldehyde 

 amounting to 6.2 per cent. The relative loss of solids from the 

 brains of 40- and of 50-day-old animals, as shown in table 10, 

 is not due to exceptional records for certain rats at these ages, 



