CHAPTER 14 

 GROWTH OF ORGANS— WILD NORWAY 



1. Brain weight on body weight, (a) Comparison with albino, (b) Cranial 

 capacity. 2. Spinal cord weight on body weight. 3. Size and shape of cerebrum, 

 (a) Comparison with Albino. 4. Growth of cortex— thickness, (a) Comparison 

 with Albino. 5. Growth of cortex— volume, (a) Comparison with Albino. G. 

 Number of cortical cells, (a) Comparison with Albino. 7. Size of cortical cells, 

 (a) Comparison with Albino. 8. Size of sympathetic cells. 9. Weight of eye- 

 balls. 10. Weights of ductless glands and gonads. 



1. Brain weight on body weight. Donaldson and Hatai ('11). 

 The direct determinations of the weight of the brain have been 

 made on 232 males and 278 females- — table 187. The general 

 formula (58) expresses the relation of brain weight on body weight 

 for the sexes combined. 



It applies however only to rats with a body weight above 5 

 grams. 



It has been found how^ever (Donaldson and Hatai, '11, p. 428) 

 that the weight of the male brain is one per cent above the mean 

 for the two sexes, and that of the female, one per cent below. 



As a consequence, each value gotten by the foregoing com- 

 putations has been corrected by adding one per cent to the value 

 found to give the weight for the male brain and by subtracting 

 one per cent to obtain the weight for the female brain. 



Chart 64 gives the graph for the male brain weight on the body 

 weight and the corresponding graph (male) for the Albino is also 

 drawn for comparison. The marked difference in the brain weight 

 of the two forms is clearly shown. 



(a) Comparison with the albino. Utilizing the data in tables 

 144 and 187 and using those for the albino male as the standards 

 in each instance, it is found that the brain weight of the Norway 

 male exceeds that of the Albino for the same body weight or body 

 length by the percentages given in table 192. 



358 



