160 FRANKLIN C. McLEAN 



infection has occurred, evidence of inflammation is added to the picture 

 of edema. 



The edematous tissues are swollen, permit fluid to escape on incision, 

 and are inelastic, retaining the impress of one's fingers on pressure. This 

 condition may be observed in the organs at autopsy, but it is generally most 

 striking in the subcutaneous tissues. The edematous organs or tissues are 

 found to have lost much of their opacity, and may appear almost agate- 

 like. This is seen especially in the lungs and in fibrous and muscular 

 tissues, such as the walls of the intestines and gall-bladder, the pelvis of 

 the kidneys, and the subcutaneous tissues in general. 



Microscopically there may be seen clear spaces in or between the cells 

 of the organs. In cases of long standing there may be evidence of sec- 

 ondary retrogressive changes. 



The Chemistry of Edema Fluids. Edema fluids, when non-inflamma- 

 tory in origin, are known as transudat.es. They vary in composition in 

 different parts of the body, and in different conditions, but in general 

 they resemble the composition of the blood plasma of the same individual, 

 with the exception that they are much poorer in proteins. The specific 

 gravity, which varies directly with the protein content, is usually below 

 1.015. Exudates, or fluids of inflammatory origin, have usually a higher 

 protein content and a higher specific gravity, generally above 1.018, but 

 the content in non-protein constituents of exudates, as well as of transu- 

 dates, resembles closely that of the blood plasma. 



For the sake of comparison with pathological tissue fluids and lymph, 

 together with the consideration of the chemistry of edema fluids, the 

 chemistry of normal lymph must be briefly reviewed. For this purpose 

 we are concerned chiefly with analysis of lymph obtained from the 

 peripheral lymph vessels, or from the thoracic duct during fasting, since 

 the composition of lymph from the thoracic duct is considerably modified 

 during absorption from the small intestine. Lymph from the peripheral 

 lymph vessels, or from the thoracic duct during fasting, is usually water 

 clear, of a yellowish green or grayish yellow color. It flows easily, and 

 has a specific gravity of 1.016 to 1.023. Jt coagulates rapidly on standing. 

 It is poor in total solids, containing from 3.8 to 5.7 per cent, the variation 

 depending chiefly on the protein content. 



The protein constituents of edema and of normal lymph include all of 

 the fractions found in the blood plasma, although not necessarily in the 

 same relative proportions. Analysis of cutaneous and other effusions have 

 been published by Epstein(a) (1914), Tables I and II. These may be 

 compared with analyses of normal lymph, of which the protein content 

 averages about 3.4 per cent, the average ratio of globulin to albumin being 

 about 2.4 to 4. Epstein (6) calls particular attention to the low protein 

 content and the high proportion of globulin in the serum and serous effu- 

 sions of chronic parenchymatous nephritis. 



