362 MANUAL OF PHYSIOLOGY. 



nutrient material passes through a special set of vessels called 

 the lacteals or lymphatics, and in so doing has to traverse pe- 

 culiar organs called lymphatic gland?, where it is no doubt modi- 

 fied and has added to it a number of cells (lymph corpuscles) 

 which subsequently are poured into the large veins with the 

 lymph and become important constituents of the blood. 



There is a certain set of organs, which have but slight traits of 

 resemblance to one another, and in consequence of the want of 

 more accurate knowledge as to their exact function, are com- 



FIG. 157. 



Section of the Thyroid (/land of a Child, showing two complete sacs and 

 portions of others. The homogeneous colloid substance is represented as 

 occupying the central part of the cavity of the vesicles, which are lined by 

 even cubical epithelium. (Schafer.) 



monly grouped together as ductless or blood glands. Some of 

 these are doubtless nearly akin to the lymphatic glands, their duty 

 being the further elaboration and perfection of the blood. In 

 this group are commonly placed the supra-renal capsules, the 

 thyroid, the thymus, and the spleen. 



SUPRA-RENAL CAPSULE. 



With regard to the function of the supra-renal capsule we may 

 say that nothing definite is known. The cortical part is said to 

 resemble the lymph follicles in structure, while the central part, 



