340 THE LYMPH. 



tory power similar to that of the renal epithelium, and are thus 

 capable of furnishing to each tissue its proper amount and kind of 

 food. This view, however, does not preclude the possibility that 

 some of the constituents of the plasma may pass over into the lymph 

 by a simple process of filtration, and it is likely that this actually 

 occurs with the water and most of the mineral salts. 



According to its origin, then, we may expect to find certain dif- 

 ferences in the chemical composition of the lymph, and we find, as 

 a matter of fact, that such differences exist. These are, however, 

 essentially of a quantitative kind, and qualitatively we find the same 

 constituents in the lymph from the various districts as compared with 

 each other and with the blood-plasma. 



Like the blood-plasma, the lymph consists of a liquid portion, the 

 lymph-plasma, and cellular elements, the lymph-corpuscles. These 

 latter are essentially mononuclear leucocytes, and are largely derived 

 from the lymphoid tissue which abounds in the course of the lymph- 

 vessels. Red corpuscles are either lacking entirely or they are pre- 

 sent in very small numbers. They are of much darker color than 

 those of the blood, but on exposure to the air they take on the 

 bright-red color of oxy haemoglobin. According to some observers, 

 they represent transition-forms between the leucocytes and the 

 normal red corpuscles of the blood. 



In various inflammatory diseases of the serous cavities the leuco- 

 cytes may be present in very large numbers, and in extreme cases, 

 indeed, they predominate to such an extent that the liquid character 

 of the lymph may be almost entirely lost. 



The appearance of the lymph is dependent upon the number of 

 the leucocytes and the amount of fat present. As obtained from 

 fasting animals, it represents a slightly viscid, straw- or rose-colored, 

 transparent fluid. During the process of digestion, on the other 

 hand, and especially after the ingestion of much fatty food, it 

 becomes more or less opaque, owing to the admixture of the fat, 

 which is carried into the general lymph-current through the chyle, 

 viz., the lymph coming from the intestinal canal. 



The odor of the lymph, like that of the blood, is different in 

 different animals. Its taste is salty, and the reaction slightly alka- 

 line. The specific gravity varies between 1.015 and 1.021. 



The amount of lymph which is produced in the twenty-four hours 

 is largely influenced by the process of digestion. During starvation 

 a smaller amount is thus found than after the ingestion of food, and 

 it appears, moreover, that an albuminous diet causes a much greater 

 increase than one of carbohydrates. Active muscular exercise has 

 a similar stimulating effect up*on its formation. Artificially the 

 amount of lymph can be increased by the intravenous injection of 

 so-called lymphagogues, of which Heidenhain recognizes two classes, 

 viz., those which merely increase the amount of water in the lymph 

 and those which also bring about an increase of the organic solids. 

 The former include such crystalline substances like sugar, urea, 



