306 



HELEN DEAN KING 



but it is found in practically all the individual records for all 

 series of experiments. An examination of the data given in 

 tables 1 to 9 shows that in six cases the average weight increase 

 in the brains of the 50-day-old rats is greater than that in the 

 brains of 40-day animals. These facts seem to indicate that 

 some chemical change takes place in the brain at 50 days of 

 age that has not been brought out by any analysis so far made. 



TABLE 10 



The percentage of solids in brains of rats of various ages kept from four to eighteen 

 weeks in solutions of 4 per cent formaldehyde (computations made from original 

 brain weights) 



EXPERIMENTS 



Brains kept IS wks. in neu- 

 tralized stock solutions. . . . 



Brains kept 10 wks. in sol. 5 

 mos. old 



Brains kept 10 wks. in freshly 

 made sol 



Brains kept 4 wks. in 40 cc 

 neutral sol 



Brains kept 4 wks. in 40 cc. 

 acid sol 



Brains kept 4 wks. in 20 cc 

 neutral sol 



Brains kept 4 wks. in 20 cc. 

 acid sol 



Brains kept 4 wks. in neutral 

 sol. at temp. 26°C 



Brains kept 4 wks in neutral 

 sol. at temp. 8toll°C... 



AGE OP BATS 



New- 

 born 



8.1 

 8.1 

 7.8 

 8.2 

 9.6 

 9.2 

 10.5 

 9.7 

 8.3 



Averages for above series .... 



Normal percentage of solids 

 in rats' brains (Donaldson) 



Percentage loss of solids as 

 result of action of formal- 

 dehyde 



8.6 

 12.2 



29.5 



10 

 days 



20 

 days 



10.3 i 14.7 



10.1 

 10.3 

 10.1 

 10.9 



9.8 



40 

 days 



16.5 

 16.0 

 16.4 

 16.7 

 16.2 



10.9 j 16.3 ! 19.0 



I 



9.8 15.1 18.7 



18.4 

 19.4 

 19.2 

 19.3 

 19.3 

 19.7 



10.6 



16.3 



10.6 

 14.6 



29.4 



16.3 

 17.5 



7.4 



19.2 



19.2 

 19.5 



1.5 



50 



days 



19.4 

 19.4 

 19.5 

 19.6 

 19.1 

 20.5 

 20.0 

 19.4 

 19.0 



19.6 

 20.9 



6.2 



70 

 days 



19.5 

 20.5 

 20.1 

 19.6 

 20.7 

 19.9 

 20.1 

 19.8 

 20.1 



100 



days 



19.7 

 20.1 

 20.9 

 20.1 

 20.2 

 20.8 

 20.1 

 20.1 



20.1 

 21.1 



4.7 



20.3 

 21.3 



4.7 



200 

 days 



20.9 

 20.5 

 21.6 

 21.8 

 21.1 

 21.5 

 21.6 

 20.1 

 21.7 



21.2 

 21.6 



1.8 



