CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 523 



The Characters of Lymph. 



295. As it slowly flows from its origin in the tissues to 

 the mouth of the thoracic duct (we may for simplicity's sake 

 omit the right lymphatic trunk) the lymph is subjected to the 

 influence of the lymphatic glands, and is possibly affected by the 

 walls of the lymph-vessels. Moreover the lymph coming from one 

 tissue differs more or less in certain characters from the lymph 

 arising in another tissue, just as the venous blood of one organ 

 differs from the venous blood of another organ ; and these differ- 

 ences may be exaggerated by the activity of the one or other 

 tissue. Of these differences by far the most striking is that 

 between the lymph coming from the alimentary canal during 

 active digestion and known as chyle, and the lymph coming from 

 other parts of the body. When digestion is not going on, and 

 when consequently no considerable absorption of material from 

 the alimentary canal into the lacteals is taking place, the fluid 

 flowing along the lacteals is lymph, not differing from the lymph 

 of other regions to any marked degree. 



The fluid accordingly which flows along the thoracic duct in 

 an animal which has not been fed for some considerable time may 

 be taken as illustrating the general characters of lymph. The 

 contents of the thoracic duct may be obtained by laying bare the 

 junction of the subclavian and jugular (in the dog the junction of 

 the axillary and jugular) veins, and introducing a cannula into the 

 duct as it enters into the venous system at that point. 



Lymph, so obtained, is a clear transparent or slightly opalescent 

 fluid, which in most cases when left to itself soon clots. The 

 clotting, which may be slight or may be considerable, though not 

 so pronounced as that of blood, or may be absent altogether, is 

 caused as in blood by the appearance of fibrin. The fibrin which 

 is formed is apparently identical with that of blood, and so far 

 as we know, all that has been said previously, 14 23, con- 

 cerning the nature of clotting in blood applies equally well to 

 lymph. 



Examined with the microscope lymph contains a number of 

 corpuscles, lymph-corpuscles, which in their broad features are 

 identical with white blood-corpuscles ; they vary in size from 5 //, 

 to 15 ft, the smaller corpuscles being much more abundant in 

 lymph than in blood ; and like the white corpuscles of the blood 

 differ from each other in features other than size. Like the white 

 blood-corpuscles of blood they exhibit amoeboid movements. Their 

 number varies in different animals, and, in the same animal, 

 according to circumstances ; on the whole perhaps it may be said 

 that lymph-corpuscles are about as numerous in lymph as white 

 corpuscles in blood. Even when every care is taken to avoid 

 accidental admixture with blood, lymph not unfrequently contains 



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