ANATOMY AND HISTOLOGY OF THE THYMUS GLAND 367 



specificity of the staining methods. Maximow has made a very careful 

 study of the histogenesis in rabbits, rats, and other mammals. His find- 

 ings, however, should not be accepted too literally as entirely representative 

 of the human condition. By fixing in Zenker-formol and staining with 

 eosin-azur and Giemsa's stain he obtained a good differential coloration 

 of the lymphocytes, and found that they arise through a. differentiation of 

 the neighboring mesenchymatous elements, which wander into the gland. 

 It is highly desirable that it should be ascertained, through the study of 

 the mitochondria and the reticular apparatus, whether there is a discon- 



Fig. 5. Section of cortex of human thymus illustrating: Lymphocytes (1), epi- 

 thelial cells (ep), endothelial cells (en) and erythrocytes (er) (magnification 720). 



tinuity between the properties of the cytoplasm of the epithelial cells and 

 lymphocytes. 



The small cells of the thymus possess the same basophilic cytoplasm, 

 the same power of ameboid movement, and the same sensitivity to X-rays 

 (Rudberg) as true lymphocytes. Moreover we have reason to believe that 

 they are able to transform into plasma cells and to form granular leuko- 

 cytes, as do the lymphocytes elsewhere. Neither the small cells nor 

 lymphocytes give the oxydase reaction with a-naphthol and dimethyl- 

 paraphenylenediamin. They are roughly about the same size. On degen- 

 eration they undergo similar pycnotic changes. There are no true germ 

 centers in the thymus and it is thought that most of the cell multiplication 

 takes place in the medulla. Prenant is credited with the observation that 

 the details of mitosis in the reticulum (epithelial cells) and small cells are 



