CHAPTER XII 



EDEMA 1 



As the terra edema indicates the excessive accumulation of 

 lymph (which may be either normal or modified in composition) 

 in the cells, intracellular spaces, or serous cavities of the body, 

 the problems of edema are inseparably connected with the 

 consideration of the processes of physiological formation and 

 removal of lymph. For many years the study of these processes 

 has been a favorite field of investigation by physiologists, and 

 the great battle-place of the " vitalism " and " mechanism " 

 schools ; and to this day the forces that determine the formation 

 of lymph and its subsequent absorption have not been com- 

 pletely understood. By the application of the principles of 

 physical chemistry to the problem, however, great advances 

 have recently been made, which seem to render our understand- 

 ing of both lymph-formation and its pathological accumulation 

 in the tissues much clearer and more nearly accurate than they 

 were before. We shall first consider, therefore, the physio- 

 logical formation of lymph, before taking up the subject of 

 edema. 



Composition of Lymph. Lymph consists of material derived from 

 two chief sources. The greater part consists of fluid passing out of the 

 capillaries into the tissue-spaces ; here it is modified by the addition of 

 products of metabolism derived from the tissue-cells, and by the sub- 

 traction of materials that the cells utilize in their metabolism. It is, 

 therefore, essentially a modified blood plasma, and the modifications the 

 plasma undergoes are so slight that, under ordinary conditions, lymph 

 shows on analysis no considerable differences from blood plasma, except 

 a relative poverty in proteids, due chiefly to the impermeability of the 

 capillary walls for colloids. Its quantitative composition varies greatly, 

 depending Upon the conditions under which it is collected, whether 

 during activity or rest, etc. The following tables of analyses have been 

 collected by Hammarsten: 2 



1 A complete bibliography is given by Meltzer, American Medicine, 1904 

 (8), 19 et seq., and references will be given below only when referring to 

 special points or to articles not included by Meltzer. Literature also reviewed 

 by Burton-Opitz, Jour. Amer. Med. Assoc., 1899 (32), 51, and by Ellinger, 

 Ergebnisse der Physiol., 1902 (I, Abt. 1 ), 355. 



2 Physiological Chemistry ; Amer. translation, 1904, p. 213. 



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