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, by the action of physical or 

 chemical processes, the details of which are not yet entirely under- 

 stood, makes its way through the thin walls of the capillaries, and is 

 thus brought into immediate 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 collected into small capillary spaces that in turn open into 

 definite 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. Recent work* 

 supports the view that the lymph capillaries are closed vessels simi- 

 lar 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. From the phys- 

 iological 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, and a second 

 smaller right lymphatic duct, which open into the blood-vessels, 

 each on its own side, at the junction of the subclavian and internal 

 jugular veins. While the supply of lymph in the lymph- vessels may 



* See MaCallum, " Bulletin of the Johns Hopkins Hospital," 14, 1, 1903; 

 also Sabin, " American Journal of Anatomy," 1, 367, 1902, and 3, 183, 1904. 



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