1 70 



HISTOLOGY 



structural relations are so disturbed and the channels become so ob- 

 structed that the gland breaks down. 



Where many lymph nodules are gathered together into a single mass 

 they acquire a cord-like reticulum of lymphoid tissue in addition to the 

 lymph nodules as seen in our first example. In such a lymph node 



the nodules are placed near the 

 periphery and the cord mass oc- 

 cupies the center (Fig. 151). 



The function of disposing of 

 harmful matter extends, in the 

 lymph glands, to the destruction 

 of broken-down red blood cor- 

 puscles, as well as the formation 

 of lymphocytes. This function 

 predominates in some blood 

 glands, which resemble lymph 

 glands except that where lymph 

 alone flowed into the peripheral 

 sinuses of the real lymph gland, 

 red blood flows into the sinuses 

 of this kind, and they are called 

 hfBmal glands. Their function 

 may be spoken of as blood 

 filtering. 



The largest gland of a lym- 

 phatic nature in the vertebrate 

 animals is the spleen. This 



organ may be looked upon as a collection of many somewhat special- 

 ized lymph nodules lying in a much larger mass of blood -removing 

 tissue called the splenic pulp or medulla. This splenic pulp must be 

 compared with the peripheral sinus found in the lymphatic nodule, or 

 more exactly and closely with the similar sinus found in the haemal 

 gland. 



The splenic pulp is arranged in a number of radial masses, each con- 

 taining several lymphatic nodules (here called Malpighian bodies) and 

 each supplied by an arterial branch. A vein also collects many small 

 branches which originate in the pulp and carries the blood out near the 

 point (the hilum) at which the artery entered (Fig. 152). On entering 

 the spleen pulp, each artery is closely invested with a layer of lymphatic 

 tissue which, in man, is very thin and is expanded, at certain points only 

 on the branches, to form the lymph nodules. The artery carries blood 

 to the nodule, where some of it is diverted into capillaries in the lymphatic 

 tissue, while the rest is carried distally by the arterial branches to the 



FIG. 151. A section of lymphatic tissue as it 

 ordinarily appears. Two nodules shown. 

 Lymph cords massed in homogeneous ap- 

 pearing tissue. From one of the larger 

 masses of lymph tissue near the appendix of 

 the cat. X 100. 



