LYMPH AND TISSUE FLUIDS 1013 



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 compo- 

 sition 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 about 6 per 

 cent, of solid matters, the proteins consisting of fibrinogen, paraglobulin, and 

 serum albumen. The salts are similar to those of the liquor sanguinis, and 

 are present in the same proportions. 



THE PRODUCTION OF LYMPH 



Many physiologists have thought that, in the transudation of the fluid 

 which forms the lymph, there is an active intervention on the part of the 



