708 



THE LYMPHATIC SYSTEM 



The question as to whether lymph-glands may form anew is not yet entirely settled. The 

 study of the problem is extremely difficult, because very small lymph-nodes may be normally 

 present in a certain region, yet they may escape observation until they become hypertrophied 

 under certain conditions. A. W. Meyer in a careful experimental study found no evidence of 

 new-formation of lymph glands. On the other hand, there is considerable evidence for the new- 

 formation of lymph-glands under pathological conditions. 



The haBmolymph nodes. — In addition to the ordinary lymph-nodes, there 

 occur along the course of certain veins small nodes which are either red or brown 

 in colour, according to their state of functional activity. These have been termed 

 haemolymph nodes. The red nodes closely resemble in structure an ordinary 

 tymph-node, except that the sinuses are jQUed with blood, while the brown nodes 

 show not blood, but blood pigment, both free in the sinuses and in the phagocytic 

 cells of the sinuses. In certain respects these nodes resemble the spleen, there 

 being a reduction of the medullary cords and an increase in the amount of the 

 sinuses, which resemble those of the spleen-pulp rather than the more open 

 lymphatic sinuses; and their trabeculae are also like those of the spleen in having 

 numerous smooth muscle-cells. Some of these haemolymph nodes have lymphatic 



Fig. 554.— a Developing Haemolymph Node. 



e - — Peripheral blood-sinus 



_-./! — Blood-vessel at hilus 



vessels, but whether, as in the spleen, these are limited to the capsule, or whether 

 they open into the blood-sinuses, making true haemolymph nodes, is not yet clear. 



A difficult point in connection with the structure of the haemolymph nodes is the relation 

 of the blood-sinuses to the blood-vessels. The greater weight of evidence seems to favour 

 the view that the sinuses are connected with the veins rather than that the arteries open directly 

 into them, although one ob.server fails to find any connection between the blood-vessels and 

 the central sinus (Schumacher). In fig. 554 is shown a haemolymph node in the neck of a pig 

 24.5 cm. long. This stage marks the first appearance of the haemal node in the neck, and shows 

 the node in its simplest form, the follicle and its peripheral blood-sinus (Miss Sabin). 



There are wide variations in the distribution and number of the haemolymph nodes; indeed 

 sufficient observations have not yet been made to determine their complete distribution. 

 They have been divided into three groups, the praevertebral, the renal, and the splenic. In 

 one subject, in which they were very numerous, they occurred at the root of the lung, near the 

 bronchi ana broncliial vessels, a few near the trsophagus, a continuous pricvertebral chain in 

 the abdomen extending from the diaphragm to the upper two or three sacral vertebrae, as well 

 as a few along the c(x;liac axis and its branches, the superior mesenteric, renal, and iliac vessels 

 (Lewis). 



Schumacher, from a study of lymph-glands and liaemolymph glands of various stages, 

 concludes that the haemolymph glands are not to be considered as organs sui generis, but that 

 they represent rudimentary forms of ordinary lymph-glands, which have lost their connections 

 with the lymphatic vessels. Further investigations are needed to clear up this subject. 



