Chap, i.] TISSUES AND MECHANISMS OF DIGESTION. 401 



tain number of red blood corpuscles ; sometimes these are suffi- 

 cient to give the lymph (or chyle) a reddish tinge. They have 

 been observed within the living lymphatic vessels, even within 

 small ones, and have probably in some manner or other made 

 their way from the blood into the lymph-channels. 



§ 238. The chemical composition of lymph, even when taken 

 in each case from the thoracic duct, varies a good deal. The 

 total solids are much less than in blood, amounting in general 

 to not more than 5 or 6 p.c. Hence the venous blood of a vascu- 

 lar area contains rather more solids than the arterial blood of the 

 same area, since the blood in giving rise to the lymph during 

 its passage through the capillaries from the arteries to the veins 

 has parted with relatively more water than solid matter. 



The proteids amount on the average to about 3 or 4 p.c, 

 that is to say, to about half as much as in blood, the particular 

 proteids present being the same as in blood, viz. albumin, para- 

 globulin and antecedents of fibrin. In lymph, as distinguished 

 from chyle, the quantity of fat is small, and consists 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 consider- 

 able 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. 



§ 239. Lymph may also be obtained from separate regions 

 of the body, as from the lower or upper limbs, for instance, by 

 introducing a fine cannula into a lymphatic vessel. In its gen- 

 eral features the lymph so obtained resembles that taken from 

 the thoracic duct. Analyses of the lymph distending the sub- 

 cutaneous connective tissue in cases of dropsy shew that this 

 contains 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 vessels contains aii excess 

 of water ; and indeed it has been asserted that the percentage 

 of solids increases in passing from the smaller to the larger 

 vessels ; but this cannot be regarded as distinctly proved. The 

 number of corpuscles however, as we have already said, appears 



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