THE THYMUS 333 



in young children exceeds that of the whole thymus in a three 

 months' embryo. 



It will not be possible to give a full account of the various 

 thymus elements,. One other thymic structure must, never- 

 theless, be briefly referred to. In 1888 Sigmund Mayer 

 described certain peculiar elements in the frog's thymus. 

 These he regarded as rudimentary voluntary muscle fibres. 

 Similar structures were observed in Teleosts by Schaffer, who 

 described them as sarcolytes in various stages of disintegra- 

 tion. Similar structures which have been discovered in birds 

 and reptiles are considered to be of a muscular origin and nature. 

 Hammar, however, regards them as specially differentiated 

 hypertrophic reticular cells, and therefore as closely related to 

 the concentric corpuscles. Pappenheimer has recently found 

 these myoid cells in the human embryonic thymus, and holds 

 the same view as Hammar as to their nature and origin. 



,C. Extirpation of the Thymus 



Abelous and Billard reported that the removal of both 

 thymus glands in the 



frog always resulted , f^^^^l '*e o 



fatally within three to ^9 J&* oj*&?8%- 



T7 "^ ^^& 



fourteen days. Ver ,QP 



Eecke, however, 

 pointed out that death 

 did not occur if pre- 

 cautions against inf ec - ' < .*'/' 

 tion were taken by a| o.e^ 

 regularly renewing the J* 

 water in the frog- 

 tanks. The latter in- 

 vestigator was of 

 opinion that removal 



of the thymus lowers FIG. 93. Hassall's concentric corpuscle from 



the resistance of the the human thymus gland. The concentric 



. arrangement is not so regular or so marked as 



frog to Septic mrLu- in the cat. (Drawn by Mrs. Thompson.) 



ences, and that this 



accounts for the fatality in the experiments of Abelous and 



Billard. 



The present writer came to the conclusion that in the case 



