292 



HELEN DEAN KING 



the two other brains of the group were put into the same amount 

 of solution which was not neutrahzed and which gave a faintly- 

 acid reaction when tested with litmus paper. As the second 

 series of experiments had shown that there is comparatively little 

 difference between the percentage weight increase in the various 

 sets of brains at the end of four weeks and at the end of ten weeks, 

 these experiments and all the later ones were terminated at the 

 end of one month and the brains heat dried. 



Table 4 shows the data obtained in the experiments in which 

 the brains were subjected to the action of a neutralized solution. 



TABLE 4 



Percentage weight increase in rats' brains, each kept foY four weeks in 40 cc. of a 

 neutralized solution of 4 psr cent formaldehyde made fresh for each lot of animals 

 killed (averages for two brains at each age) 



TIME SOLUTION ACTED 



1 day. . . 

 3 days . . 

 7 days. . 



2 weeks. 



3 weeks. 



4 weeks. 



AGE OP RATS 



New- 

 born 



60.4 

 65.8 

 65.4 

 65.1 

 64.8 

 61.7 



10 



days days 



54.7 



58.51 



58.5 



58.4 



58.2 



57.8 



Average percentage gain 63.4 57.7 49.2 45.9 46.4 44.8 40.3 35.8 



20 



45.8 



52.91 



48.3 



48.9 



48.9 



50.4 



40 

 days 



47.61 



47.4 



45.6 



45.3 



44.7 



45.1 



50 

 days 



50.41 



47.7 

 45.1 

 44.8 

 45.2 

 45.4 



70 

 days 



44.9 

 48.8 

 44.2 

 43.2 

 43.9 

 44.9 



100 200 



days days 



44.2 

 42.7 

 38.3 

 38.6 

 38.8 

 39.3 



36.1 



40.11 



36.2 



33.0 



34.7 



34.9 



1 Maximum weight increase. 



The data given in this table indicate that, under the condi- 

 tions of these experiments, the amount of swelling which the 

 brains undergo diminishes as the age of the animal increases. 

 Brains of new-born rats swell enormously, the average percent- 

 age increase in three days, when the maximum is reached, being 

 65.8 per cent of the original brain weight, and there is a falling 

 off of only 4 per cent at the end of four weeks. Brains of ten- 

 day-old animals gain, on an average, only about 6 per cent less 



