1134 PHYSIOLOGY 



a constant flow of lymph being the alimentary canal. And thus 

 we cannot regard the flow of lymph from a part as any index 

 of the chemical changes going on at that part. In a limb at rest 

 food-stuffs are being taken up from the blood and being burnt up by 

 the muscles with the production of C0 2 , although we may not be able 

 to obtain a drop of lymph from a cannula in one of the lymphatics. 

 The lymph is thus truly a middleman ; as any substance, oxygen 

 or food-stuff, is taken up by a tissue-cell from the lymph surrounding 

 it, this latter recoups itself at once at the expense of the blood. 

 Thus there would seem to be no need for lymphatics to drain the 

 limb, were it not that under many conditions which we shall study 

 directly, the exudation of lymph from the blood-vessels is so excessive 

 that, if it were not carried off at once and restored to the blood, it 

 would accumulate in the tissue spaces, give rise to dropsy, and by 

 pressure on the cells and blood-vessels affect them injuriously. 



PROPERTIES OF LYMPH 



Lymph obtained from the thoracic duct of an animal varies in 

 composition and appearance according to the condition of the animal, 

 whether recently fed or fasting. From a fasting animal the lymph is 

 a transparent liquid, generally slightly yellowish, and sometimes 

 reddish from admixture of blood-corpuscles. When obtained from 

 an animal shortly after a meal, it is milky from the presence of minute 

 particles of fat that have been absorbed from the alimentary canal. 

 In the latter case, if the intestines be exposed, the small lymphatics 

 are to be seen as white lines running from the intestine to the attached 

 part of the mesentery. It is owing to this fact that these lymphatics 

 have received the special name lacteals, the lymph in them being called 

 the chyle. The fatty particles form the molecular basis of the chyle. 



On microscopic examination the transparent lymph of fasting 

 animals presents colourless corpuscles similar to those of blood, or 

 perhaps we ought to say identical, since the leucocytes of the blood 

 are partly derived from the corpuscles that have entered with the 

 lymph through the thoracic duct. 



All the lymphatics pass at some point of their course through 

 lymphatic glands, which we may look upon as factories of leucocytes, 

 since these are much more numerous in the lymph after it has traversed 

 the gland than before. Leucocytes are also formed in all the numerous 

 localities where we find adenoid tissues, such as the tonsils, air passages, 

 alimentary canal (Peyer's patches and solitary follicles), Malpighian 

 bodies of the spleen, and thymus. 



The lymph from the thoracic duct is alkaline, has a specific gravity 

 of about 1015, and clots at a variable time after it has left the vessels, 

 forming a colourless clot of fibrin, just like blood-plasma. It contains 



