512 NAOKI SUGITA 



to compare the results in these valuable papers, because, the 

 authors are not in accord in respect to technical methods or the 

 localities where the thickness was measured. My intention in 

 the study which follows is to present the results of the exact 

 measurements systematically applied to the thickness of the 

 cerebral cortex during postnatal growth, using ample material 

 and treating this with uniform methods of dissection, fixation, 

 imbedding and staining. The systematic examination of sec- 

 tions thus prepared should make it possible to trace the steps in 

 the growth of the cerebral cortex of the albino rat from birth to 

 maturity in a way which could be controlled by subsequent 

 workers in this field. 



Hitherto, there has been no systematic study in this field so 

 that I have not had any previous example to follow. I have 

 therefore used my own judgment as to the localities to be sec- 

 tioned and the methods of measurement. The reasons for the 

 various methods will be given in the appropriate chapters. In 

 a later part of this series of studies, I shall try to review col- 

 lectively the data presented by previous authors concerning the 

 cortical thickness of human and animal brains. As these re- 

 searches have, however, been all directed towards the solution 

 of phylogenetic problems and have been made on the adult 

 individual, they have but little immediate bearing on the present 

 problem. 



In connection with this research, and using the same material, 

 I have studied also the developmental changes during growth in 

 the size and shape of the ganglion cells, the differentiation of the 

 cell-layers of the cortex, the distribution of the several kinds of 

 ganglion cells in the cerebral cortex, and further, the changes in 

 the relations between the elements of the central nervous system 

 according to the growth phase of the brain. These results Avill 

 be presented in papers which are to follow. 



This study was started in October, 1915, and completed in 

 June, 1916, under the direction of Prof. H. H. Donaldson at The 

 Wistar Institute of Anatomy and Biology and I am much in- 

 debted to Prof. Donaldson for his valuable suggestions. 



