GROWTH OF THE CEREBRAL CORTEX 553 



In two brains of the same age and treated by the same method, 

 the ratio between any diameter measured on the fresh brain and 

 that measured after imbedding in paraffine is ahnost constant, 

 although heavier brains suffer shghtly more shrinkage. But the 

 ratio between a gi^'en diameter on slide and the same diameter 

 in paraffine block has proved less constant, probably because, as 

 mentioned earlier, on extending or unfolding the sections on 

 slides the results are modified by slight differences in the tem- 

 perature applied or in the duration of heating. I could not avoid 

 this irregularity, though I endeavored to do so. These minor 

 effects of the technique might be ignored in case of purely histo- 

 logical or pathological investigations, which aim only to detect 

 changes in the formal aspects of the elements of tissue and do 

 not regard the minute changes in size caused by the technique; 

 but in the present study which requires painstaking exactness at 

 every point, some effort must be made to correct for these 

 changes. 



At the beginning of this study, it was appreciated that such 

 changes would occur, and the necessary preliminary observa- 

 tions were made (Sugita, '17). On the fresh rat brain I measured 

 in each case the following diameters to 0.05 mm. by placing the 

 brain on the glass-plate, basal surface down. Figure 12 gives 

 the position of these diameters. 



1. Width AB, (W.B,) the greatest width along the frontal 

 plane. 



2. Width CD, (W.D), passing through the middle point of the 

 fissura sagittalis and parallel to AB. This corresponds to the 

 plane in which the frontal sections were taken. 



3. Length EF, (L.F), passing through the frontal pole and 

 running parallel to the mesial surface of the hemisphere. This 

 corresponds to the plane of the sagittal sections. 



4. Length EG, (L.G), passing from the frontal pole at E to 

 the occipital pole at G. This measurement gives the greatest 

 length. 



5. Height HK, {Ht), (fig. 12 b) from the stalk of the hypoph- 

 ysis to the dorsal surface and vertical to the basal surface of 

 the brain. 



