460 J. A. BADERTSCHER 



gone changes. The medulla of the lobes, in some of which at 

 this stage it is but slightly developed, is continuous with that of 

 the central stem. The deep portions of some of the interlobular 

 septa are almost in contact with it while others are separated 

 from it by a cortical layer of considerable thickness. The 

 medulla is formed directly from the epithelial syncytium. In 

 sections stained with Hasting's Nocht's stain it is easily dis- 

 tinguished from the cytoplasmic syncytium of the cortex by its 

 brighter red color. The initiative changes marking its appear- 

 ance are apparently chemical in their nature as pointed out by 

 Bell, for the syncytium in some parts of the central stem and 

 in the center of some of the lobules is stained a bright red even 

 before any morphological changes have set in. The morphologi- 

 cal changes of the epithelial structure occur very soon after, or 

 almost simultaneously with, the chemical changes. The epithe- 

 lial cells hypertrophy. The nuclei become large and relatively 

 clear when compared with those of the cortex. The cytoplasm 

 of the syncytium also increases in amount. Its anastomosing 

 processes are no longer thin and attenuated as they now appear 

 in the cortex but have become more or less massive bands. 

 Although the cortex and medulla are quite sharply defined the 

 cytoplasmic processes of the epithelial cells lying along the 

 line of demarcation between these two structures are contin- 

 uous with each other. 



Soon after the medulla has started to develop some of the 

 epithelial nuclei contained in it greatly increase in size, grow- 

 ing much larger than the majority of hypertrophied nuclei. 

 These may be found singly or in groups of two or three and 

 mark the beginning -of Hassall's corpuscles. 



All the different types of lymphocytes (large, medium-sized, 

 and small) found in the cortex are also found scattered in the 

 meshes of the reticulum of the medulla where they are, how- 

 ever, much less numerous than in the former place. According 

 to Maximow ('09 b) the disappearance of the lymphocytes from 

 the medulla, when it is first formed, is due to their migration 

 into the cortex and to degeneration. His interpretation does not 

 seem to explain similar conditions existing in the thymus of the 



