CHAPTER XXIV. 

 COMPOSITION AND FORMATION OF LYMPH. 



Lymph is a colorless liquid found in the lymph- vessels as well 

 as in the extravascular spaces of the body. All the tissue elements, 

 in fact, may be regarded as being bathed in lymph. To understand 

 its occurrence in the body one has only to bear in mind its method 

 of origin from the blood. Throughout the entire body there is a 

 rich supply of blood-vessels penetrating every tissue with the ex- 

 ception of the epidermis and some epidermal structures, as the nails 

 and the hair. The plasma of the blood makes its way through the 

 thin walls of the capillaries, and is thus brought into immedi- 

 ate contact with the tissues, to which it brings the nourishment 

 and oxygen of the blood and from which it removes the waste 

 products of metabolism. This extravascular lymph is col- 

 lected into small capillary spaces which, in turn, open into defi- 

 nite lymphatic vessels. It is still a question among the his- 

 tologists whether the lymph- vessels form a closed system or are in 

 direct anatomical connection with the tissue spaces. Modern 

 work* supports the view that the lymph capillaries are closed 

 vessels similar in structure to the blood capillaries. They end 

 in the tissues generally, but are not in open communication with 

 the spaces between the cellular elements or with the larger serous 

 cavities between the folds of the peritoneum, pleura, etc., or 

 with the spaces between the meningeal membranes surrounding 

 the central nervous system. From the physiological standpoint, 

 however, the liquid in these latter cavities, the cerebrospinal 

 liquid and the liquid bathing the tissue elements, must be 

 regarded as a part of the general supply of lymph and as being 

 in communication with the liquid contained in the lymph- 

 vessels. That is to say, the water and the dissolved substances 

 contained in the tissue spaces interchange more or less freely 

 with the lymph proper found in the formed lymph-vessels. The 

 lymph-vessels unite to form larger and larger trunks, making 

 eventually one main trunk, the thoracic or left lymphatic duct, 



* See Sabin, "American Journal of Anatomy," 1, 367, 1902, and 3, 183, 

 1904; also " General and Special Anatomy of the Lymphatics," from Poirier 

 and Charpy, translated by Leaf, 1904. 



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