CHAPTER XIV 



THE LYMPH, AND INTERCHANGES BETWEEN THE BLOOD AND 



THE TISSUES 



CONTENTS. 1. Structure of lymphatic vascular system, lymph spaces, 

 sinuses and cavities. 2. Origin ; physical, morphological and chemical char- 

 acteristics ; qualitative and quantitative variations of lymph. 3. Lymphatic 

 circulation, and the various mechanical factors by which it is determined. 



4. Formation of lymph from the blood capillaries, and the so-called lymphagogues. 



5. Secretory theory of Heidenhain, and transudation theory of Cohnheim. 



6. Formation and modification of lymph by the tissues. 7. Lymphoid tissue, 

 follicles and lymphatic glands. 8. Bone marrow. 9. The thymus. 10. The 

 spleen. Bibliography. 



No less important than the gas exchanges between the blood 

 and the tissues, to the life of the cells of which the latter consist, 

 is the exchange of solid matters in which the blood yields to the 

 tissues the substances necessary to their nutrition and restoration 

 (histogenic substances), and the tissues yield to the blood the 

 products of their elaboration, transformation, or consumption 

 (histolytic substances, anabolic and katabolic.) 



The nutritive, like the respiratory, exchanges are almost 

 invariably accomplished by means of the lymph, which is the true 

 internal medium in which the elements of the tissues live. 

 Hence the study of the nutritive exchanges includes the study of 

 the lymph ; of the functions of the lacunar and vascular system 

 which contain it ; of the functions of the tissues and organs which 

 more particularly contribute to its formation and modifications ; 

 of the mechanical factors that are constantly setting it in motion 



/ o 



and renewing it, driving it out into the blood torrent. All these 

 will be discussed in the present chapter. 



I. The Lymphatic System, discovered by Aselli, Pecquet, 

 Piudbeck, Bartholin, in the first half of the seventeenth century 

 (see Chap. VI. 6), is one of the most extended and most important 

 in the body. It embraces, not only the vessels, follicles, and 

 lymphatic glands, but also the whole of the connective tissues, 

 and the system of lacunae or interstitial spaces which exist in 

 every part of the body, particularly where there are more or less 

 loosely constituted connective tissues. Even the large serous 



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