Watson, WeigJit of the Nervous System. 523 



increase in the body weight of Groups B and C as compared 

 with D and E (A being omitted : see note p. 521) of both the 

 mated and unmated series, we find that in this case the increase 

 of one gram of body weiglit is accompanied in the mated series 

 by .0032 gr. and in the unmated series by .0012 gr. increase 

 in the weight of the cord or on the average by .0022 — nearly 

 the value found from the laboratory records. If, then, we con- 

 sider that the removal of the excessive fat on the mated series 

 would reduce its body weight to 219.5 gr. when the animals 

 were in the same condition as the unmated series, then the dif- 

 ference in body weights between the two series amounts to 8.7 

 gr. which would call for .0191 gr. additional cord weight in the 

 heavier animals. The observed difference in the two series is 

 .6317 — 6025 gr. , or .0292 gr., which serves to show that the spin- 

 al cord of the mated rats is heavier than we should expect from 

 their true body weight. Whether this excess has resulted from 

 changes affecting the entire cord or only the lumbar regions, 

 was not determined. 



5. The brain and spinal cord of the mated individuals 

 contained a slightly higher percentage of water. Only a single 

 exception to this relation was found in the entire series of ten 

 groups, namely in the case of the spinal cord in Group C. 



6. In general the older groups had smaller brain weights 

 than the younger. The diminution in brain weight according 

 to age is nearly proportional in the mated and unmated groups. 

 This change probably marks the beginning of senescence. 



Resume. 



The effect of the bearing of young is to render the mated 

 rats slightly heavier than the unmated — some of the excessive 

 weight being due to the larger amount of fat present in the 

 mated animals. The proportional brain weight is not appreci- 

 ably affected, but the spinal cord is distinctly heavier in the 

 mated series, thus making the central nervous system as a 

 whole heavier. The percentage of water in both the brain and 

 spinal cord is in nine cases out of ten greater in the mated 

 groups. This is perhaps the most important difference estab- 



