316 THE TISSUES AND MECHANISMS OF DIGESTION. 



The proteids amount on the average to about 3 or 4 per cent., that is to 

 say, to about half as much as in blood, the particular proteids present being 

 the same as in blood, viz., albumin, paraglobulin and antecedents of fibrin. 

 In lymph, as distinguished from chyle, the quantity of fat is small, and con- 

 sists of the usual neutral fats and the soaps of their fatty acids, together 

 with lecithin ; cholesterin may also be present. A certain amount of sugar 

 (dextrose) appears to be always present, and several observers have found 

 an appreciable quantity of urea. The ash of lymph like that of blood-serum 

 contains a considerable quantity of sodium chloride, while phosphates and 

 potash are scanty ; it also contains iron, apparently in too great a quantity 

 to be accounted for by the few red corpuscles which may be present. From 

 lymph a certain amount of gas can be extracted, consisting chiefly or almost 

 exclusively of carbonic acid, with a small quantity of nitrogen, the amount 

 of oxygen'present being exceedingly small. The importance of this we shall 

 see when we come to study respiration. 



Broadly speaking, we may say that all the substances present in blood- 

 plasma are present also in lymph, but are accompanied by a larger quantity 

 of water. 



250. Lymph may also be obtained from separate regions of the body, 

 as from the lower or upper limbs, for instance, by introducing a fine canula 

 into a lymphatic vessel. In its general features the lymph so obtained re- 

 sembles that taken from the thoracic duct. Analyses of the lymph distend- 

 ing the subcutaneous connective tissue in cases of dropsy show that this con- 

 tains much less solid matter than normal lymph taken from the thoracic duct 

 or larger lymphatic vessels. From this it has been inferred that the lymph 

 normally existing in the lymph-spaces, lymph-capillaries and minute ves- 

 sels contains an excess of water ; and, indeed, it has been asserted that the 

 percentage of solids increases in passing from the smaller to the larger ves- 

 sels ; but this cannot be regarded as distinctly proved. The number of cor- 

 puscles, however, as we have already said, appears to be increased in passing 

 through the lymphatic glands. It has also been stated that the lymph in 

 the finer lymph-vessels clots even less firmly than that in the thoracic duct. 

 From this we may infer that some of the leucocytes in the adenoid tissue 

 of the follicles of a lymphatic gland find their way into the lymph-sinus, 

 and so into the efferent lymphatics, and that some of the fibrin factors are 

 added to the lymph, or, at least, that some changes favorable to clotting are 

 brought about. 



251. The large serous cavities of the peritoneum, pericardium, etc., 

 are parts of the lymphatic system ; indeed, pericardial or other serous fluid 

 has all the general characters of lymph. We have already said ( 20), that 

 these fluids, when taken fresh from the body, clot (this is, at least, the case 

 in most animals) ; the clot, when examined microscopically, is found to con- 

 sist of colorless corpuscles like those of lymph or of blood entangled in the 

 meshes of fibrin. Both in their proteid and other chemical constituents these 

 serous fluids resemble lymph. Analyses of the accumulations of fluid occa- 

 sionally occurring in these cavities show that they contain sometimes less and 

 sometimes more solid matter than ordinary lymph. The aqueous humor of 

 the eye contains very little solid matter ; and the cerebro-spinal fluid is so 

 peculiar that it had better be considered by itself in connection with the 

 nervous system. 



252. Chyle. In fasting animals the fluid flowing along the lacteals, 

 as may be seen by inspection of the mesentery, is clear and transparent ; it 

 is lymph, differing, as we have said, in no essential respects from the lymph 

 flowing along other lymphatic vessels. Shortly after a meal containing fat 

 (and every meal does contain some fat), the lymph becomes white and 



