CIRCULATION OF LYMPH 111) 



number of leukocytes; accidentally, red corpuscles and blood 

 plates; after meals, fat globules. Lymph contains the pro- 

 teins, the extractives, and the salts of blood. The last are in 

 the same proportions as in blood; the proteins and especially 

 the fibrinogen are present in lesser amounts. Lymph coagu- 

 lates more slowly and less firmly than blood. During digestion 

 there is a marked increase in fats in the lymph of the intestine, 

 making it resemble milk, and it then becomes known as chyle. 

 The lymph derives substances from three sources from the 

 blood, from the tissues, and from the villi of the intestines. 

 The fluid which fills the interstices of the tissues is not in open 

 communication with the lymph in the lymph capillaries. The 

 latter, ramifying the tissues, end blindly in single-layered 

 endothelial walls. From the capillaries the lymph is passed 

 into definite lymphatic vessels which finally empty their con- 

 tents into the bloodvessels at the junction of the subclavian 

 and internal jugular veins. 



The lymph, in moving from the tissue gaps and lymph 

 capillaries to the veins, passes from a point of relatively high 

 pressure to one of low pressure. The pressure in the lymph 

 capillaries has been estimated at from 12 to 25 mm. Hg; in 

 the thoracic duct, near its entrance into the veins, it is very 

 near to zero, and often is negative. In some of the lower ani- 

 mals there are separate lymph hearts which act as force-pumps 

 to drive the lymph on. In man such lymph hearts do not 

 exist, but the movement is brought about by other factors: 



1. By the continual formation of new lymph. 



2. By the muscular movements of the body compressing 

 the lymphatics, which force the lymph on in the proper direc- 

 tion, the reverse flow being prevented by valves. The chyle 

 is aided in its flow by the action of the muscular fibers of the 

 small intestine and also by the contractions of the villi. In 

 the mouse the chyle has been seen to flow with the intermittent 

 movements corresponding to the peristaltic waves. The con- 

 tractility of the walls of the lymph vessels themselves probably 

 aids the flow. 



3. The thoracic aspiration of the chest on inspiration draws 

 the lymph into the thoracic cavity in the same manner as 

 it draws the venous blood. The movement of the lymph is, 

 without doubt, irregular, but in the course of a day a con- 



