FURTHER STUDIES OF THE HISTOLOGY OF THE 



THYMUS 



ALWIN INI. PAPPENHEIMER 



From the Marine Biological Laboratory, Woods Hole, Mass., and the Department of 

 Pathology, College of Physicians and Surgeons, Columbia University, 



New York 



TEN FIGURES (FIVE PLATEs) 



The conception ' of the thymus gland as an organ of internal 

 secretion rests almost wholly upon the facts obtained from physi- 

 ological experiment. In the thyroid, parathyroid, hypophysis 

 and adrenal, we have clear morphological evidence of secretory 

 activity on the part of the parenchymal cells. But this is not 

 true in the case of the thymus, and we do not even know which 

 of the complex elements of the gland contribute the hypothetical 

 secretion. The following study of the frog's thymus was under- 

 taken primarily in the hope of throwing some light upon this 

 problem, by the use of methods which have not hitherto been 

 applied to a study of the thymus; namely, stains for the demon- 

 stration of cell granulae, and the study of the living cells grown 

 in vitro after the method elaborated by Harrison, Burrows and 

 Carrel. The findings in the fixed tissue were checked up and 

 amplified by applying various vital stains to the living cells in 

 cultures. The work includes also a comparative study of the 

 growth of thymus and lymph-node in vitro. Because of the 

 absence of suitable lymphoid tissue in the frog, the observations 

 were made on tissue obtained from young rats. 



It may be admitted at the outset that clear-cut morphologi- 

 cal evidence of a secretory function on the part of any of the 

 thymic elements, has not been obtained. The observations 

 which were made serve, however, to clarify some of the contro- 

 versial points in the normal structure of the organ and add some 

 new histological details which seem to justify their publication. 



299 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 14, NO. 3 

 MARCH, 1913 



