DUCTLESS GLANDS. 365 



blood from the artery and vein of the organ, while the ordinary 

 circulation is going on, or immediately after the removal of the 

 organ, by causing an artificial stream of blood to flow through 

 it ; then the changes brought about in the blood by its passage 

 through the organ will give the required information. It can be 

 seen, from the foregoing enumeration of processes, that some 

 organs have a double function as regards the blood. Thus, in the 

 lung there is both renovation by taking in oxygen, and purification 

 by getting rid of carbon dioxide. The textures in their internal 

 respiration take the nutriment and oxygen, and give to the blood 

 CO 2 and various other waste products of tissue change. 



DUCTLESS GLANDS. 



In the preceding chapters the chief sources of income to the 

 blood, viz., the alimentary tract and the lungs, have been con- 

 sidered ; and the changes the blood undergoes in its passage 

 through the tissues in the systemic capillaries have been alluded 

 to. The elimination of one of the most important outcomes of 

 tissue change, namely, CO 2 , has been described. 



It has, further, been shown that a great part of the absorbed 

 nutrient material passes through a special set of vessels called 

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

 peculiar organs called lymphatic glands, where it is no doubt 

 modified 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 

 commonly 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 suprarenal capsules, the 

 thyroid, the thymus, and the spleen. 



