CORTICAL cells: WILD NORWAY 367 



computed number in the Norway exceeds that m the albmo by 

 1.3 per cent. This may be considered as practical equahty, so 

 that the number of nerve cells in the cortex of the two forms is the 

 same, as was suggested by Donaldson and Hatai ('11). It is of 

 interest to note that the maximum number is found in both 

 forms at a brain weight of 1.829 gms. This corresponds to 

 about 100 days of age in the albino. Thus a loss of cortical 

 cells in later life is clearly indicated. 



7. Growth in the diameters of the cortical cells and their nuclei — • 

 Sugita {'IS c). Followmg the same methods which were employed 

 for the Albino (figures 9 and 10) the growth of the largest cells in 

 unit areas of the lamina pjTamidalis and the lamina ganglionaris 

 of the cortex of the Norway rat has been determined and the 

 results are given in table 199 and in chart 67. 



(a) Comparison icith Albino. If the anomalous value for the 

 nuclei m the cells in the lamina ganglionaris of the heaviest 

 brain is excluded from the discussion, we find approxunately the 

 same growth relations in the Norwaj^ which have been recorded 

 for the Albino. Rapid growth comes to an end at the weaning 

 time and after this the cells of the lamina ganglionaris continue 

 to increase somewhat in diameter while those in the lamina 

 pyramidalis dimmish. There are however some differences. As 

 the data show (chart 67) the end of the rapid growing period in the 

 ganglion cells appears in the Norway a little after the correspond- 

 ing period in the pyramidal cells — whereas in the Albino these 

 relations are reversed. The cells in both layers are larger in the 

 Norway than in the Albino. When these are compared in size 

 for like brain weights the relations found are as in table 200. 



8. Cells in superior cervical sympathetic ganglion: Ping {'21a) 

 Norway rat. Using 85 individuals of which 22 were cage bred at 

 The Institute and 63 were caught wild about Philadelphia, Ping 

 ('21a) examined the growth of the largest cells in the superior 

 cervical sympathetic ganglion. 



These cells grow rapidly during the first 25 days after birth and 

 then more slowly, but on like body weight there is no sex difference 

 in cell size. There are somewhat more cells pigmented than in the 

 Albino — especially in the older animals- — ^but the amount of pig- 



