THE DUCTLESS GLANDS 



parenchyma, with elimination of function, comes on at about 

 fifty to sixty years of age. 



It seems, then, that we must regard the thymus as an organ 

 regularly present, and probably in an active functional con- 

 dition up to the age of puberty. The explanation offered 

 by Hammar of the opposite conclusion reached by former 

 anatomists is this : Wharton in the seventeenth century 

 observed that a reduction in size of the thymus frequently 

 occurred in exhausting or wasting diseases. This has been 





H.c.. 



; 









H.c. 



FIG. 91. Portion of the thymus gland of a monkey, as seen under a low 

 power of the microscope. (Drawn by Mrs. Thompson.) 



c., cortex ; H.c., Hassall's concentric corpuscles ; m., medulla. 



frequently noted, and so it has been customary to look upon 

 the thymus as a kind of ' ' barometer ' ' to indicate the state 

 of nutrition. But more often the mistake has been made 

 of confusing this * ' accidental involution ' ' with the age involu- 

 tion. 



It seems somewhat doubtful whether we are to look upon 

 the thymus in its fully developed condition as a lymphoid 

 organ. According to Wiedersheim, " Jedenfalls stellt die 

 thymus zu^keiner zeit ein ' lymphoides Organ ' dar." Ham- 

 mar has brought forward evidence that, not only in its origin, 



