THE LYMPHATIC SYSTEM. 



THE lymphatic system 1 includes the lymphatic vessels and lymph nodes or 

 lymphatic glands. The lymphatic vessels of the small intestine receive the special 

 designation of lacteals or chyliferous vessels; they differ in no respect from the 

 lymphatic vessels, except that during digestion they contain a milk-white fluid, 

 the chyle. 



It is now generally held that the lymphatic system is a closed system peripher- 

 ally, and that the tissue spaces are not in direct communication with lymphatics, 

 although Mall has shown that granules injected into the portal vein are returned 

 by both lymphatics and veins. Elsewhere, apparently, the absorption ^1 the 

 lymph as carried on by transudation through the endothelial lining of the lymph 

 vessels and not by permanent openings (the so-called stomata) between the endo- 

 thelial cells. ^* 



The tissue spaces (lymph spaces) are found in practically all tissues and organs, 

 and may be classified as pericellular or intercellular, perivascular and perineural 

 spaces, which are not lined by endothelium. The lymph exudes into these spaces 

 out of the blood capillaries and transudes into the lymphatic capillaries wherever 

 such exist. Spaces like the subdural and subarachnoid, and the serous cavities 

 of the body (pleural, pericardial, peritoneal, synovial bursa?) are lined by endo- 

 thelium, through which the lymph transudes by osmosis, while the lymphocytes 

 may actually traverse the membrane. The ventricles of the brain and the central 

 canal of the spinal cord, lined by the ependyma, contain a similar fluid derived 

 from the plasma of the blood in the choroid plexuses, and they communicate with 

 the subarachnoid space through the foramen of Magendie and those of Key and 

 Retzius. 



Lymph is a transparent, colorless or slightly yellow fluid of a specific gravity 

 of 1.015, more dilute than the blood plasma from which it is derived, containing 

 only about 5 per cent, of proteins and 1 per cent, of salts and extractives. It 

 contains formed elements of the lymphocyte class, and is slightly coagulable. 



Chyle is the intestinal lymph which is of a milky appearance during digestion 

 on account of the emulsified fats absorbed by the lacteals. 



The lymphatic vessels are arranged into a superficial and a deep set. On the 

 surface of the body the superficial lymphatic vessels are placed immediately beneath 

 the integument, accompanying the superficial veins; they join the deep lymphatics 

 in certain situations by perforating the deep fascia. In the interior of the body the 

 lymphatics lie in the submucous areolar tissue throughout the whole length of 

 the gastropulmonary and genitourinary tracts, and in the subserous tissue of the 

 thoracic and abdominal cavities. In the cranial cavity the perivascular sheaths 

 are lymph spaces. A plexiform network of minute, closed, capillary lymphatics 

 may be found interspersed among the proper elements and bloodvessels of the 

 several tissues, the vessels composing which, as well as the meshes between them, 

 are much larger than those of the capillary bloodvessel plexus. From these 

 networks small collecting vessels emerge, pass to a neighboring node, and divide 



1 In the revision of the section on the lymphatic system, the editor has consulted the work by Poirier and 

 Cuneo, translated by Cecil H. Leaf, 1904; the articles by Sabin, Lewis, and Heuer in the American Journal oi 

 Anatomy, February 1, 1909; and the articles by Huntington, McClure, and others (symposium) in the Anatom- 

 ical Record, May, 1908. Consult also G. S. Huntington and C. F. W. McClure, on the Anatomy and Develop- 

 ment of the Jugular Lymph Sacs in the Domestic Cat (Felis domest'ca), American Journal of Anatomy, April, 

 1910, vol. x, No. 2. 

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