LYMPH 251 



tissues with a suitable medium for their activities, and carries to them 

 the food material necessary for such activities and for repair ; carrying 

 also bodies such as hormones or co-enzymes, which stimulate or aid 

 tissue activity. From the tissues it carries away the products of 

 their activity either synthetic, such as internal secretions and hor- 

 mones, or the katabolic or waste products resulting from such activity. 



In regard to the digestive tract, the tissue fluid acts as a transport 

 fluid for the absorbed products of digestion. Some of these, such 

 as those of protein and carbohydrate digestion, pass into the blood 

 of the portal vein. The products of fat digestion, on the other hand, 

 pass into the closed lymphatic vessel, or lacteal. They give to the 

 lymph a milky appearance, from which the name of these particular 

 lymph channels is derived. 



In other parts of the body, also, there is the same quick transference 

 of some bodies from the tissue fluid to the blood, and of others to the 

 lymph. In discussing the processes of lymph formation (see later), 

 this point must be borne in mind. For example, when a salivary 

 gland is secreting, we must inquire what processes determine the 

 bodies which pass (1) from the gland to the saliva, (2) into the tissue 

 fluid, (3) from the tissue fluid to the venous blood, (4) from the tissue 

 fluid into the lymph leaving the gland. 



The properties of lymph are generally studied by collecting the 

 fluid as it flows from the thoracic duct of a small mammal, or from 

 the main lymphatic channel of each of the various organs of the larger 

 domestic animals. For demonstration purposes, a cannula is usually 

 placed in the thoracic duct of a fair-sized fasting dog, and a good flow 

 of lymph insured by the intravenous injection of commercial peptone 

 solution. Such lymph is a viscid, opalescent fluid, faintly alkaline 

 in reaction, specific gravity 1010 to 1020. The first lymph which 

 flows coagulates spontaneously, although less quickly than blood. 

 After a time, however, owing to the effect of the peptone, it becomes 

 incoagulable. Chemically, it contains the same constituents as blood - 

 plasma, the differences being quantitative. It is poorer in proteins, 

 and richer in water and salts. 



The lymph from different parts varies in quantitative composition. 

 For example, that from the liver contains more solids than that from 

 the limbs. The lymph flowing from the same organ also varies quan- 

 titatively in composition according to the degree of activity of the 

 organ. As a result of various analyses, the composition of lymph 

 may be given somewhat as follows : 



Per Cent. 

 Water . . 93-5 95-8 



Solids 4-2-0-5 



Proteins 3-5 4-I* 



Fats 'i 



?? a P?, . . 0-4-U-9 



Lipoids 



Dextrose ) 



Salts (chiefly NaCl) . . . . 0-70-8 



0-2 . . . . . . . . . . tracen 



C0 2 370 5 vols. 



