372 CIRCULATION OF CHYLE AND LYMPH. 



diminished through removal of a moderate amount of fluid, (d) In 

 those vessels that arise by means of fine secretory canaliculi, the move- 

 ment will depend directly on the tension of the parenchymatous fluids, 

 and the latter, in turn, upon the tension in the blood-capillaries. Thus 

 the blood-pressure will still be active as a force from behinde ven into 

 the lymphatic radicles. 



In the lymph-trunks themselves, the contractions of their mus- 

 cular walls propel the current onward. Heller noted, in the lymphatics 

 of the mesentery of the guinea-pig, that this movement was peristaltic 

 in an upward direction. The large number of valves prevent a back- 

 ward current. In addition, the contractions of the surrounding muscles, 

 further, any pressure upon the vessels and the tissues as the seat of 

 origin of the lymphatic radicles will force the current onward. If the 

 escape of blood from the veins is rendered difficult, lymph is poured 

 out more abundantly from the tissues in question. 



The interposed lymph-glands offer considerable resistance to the 

 current, as the lymph must flow through numerous spaces, traversed by 

 fine meshes and partially filled with cells. Nevertheless the obstacles 

 thus presented are in part compensated for by the numerous unstriated 

 muscles that are present in the sheath and the trabeculae of the glands. 

 By means of these, compression of the glands (as of a sponge) can take 

 place, the presence of the valves again determining the centripetal 

 direction of the current. From this point of view electrical stimulation 

 of swollen lymph-glands might be successful. 



With the union of the vessels into a few of considerable size, and 

 finally to form the main trunk, the sectional area of the current becomes 

 diminished, and the velocity of the current correspondingly increased. 

 Nevertheless, the velocity under such circumstances is always low, 

 reaching only from 238 almost to 300 mm. in a minute in the main 

 cervical lymph-trunk in the horse, a fact that is indicative of the 

 exceedingly slow movement of the lymph in the small vessels. The 

 lateral pressure in the same situation was from 10 to 20 mm.; in the 

 dog only from 5 to 10 mm. of a dilute soda-solution, but in the tho- 

 racic duct of a horse it was 12 mm. of mercury. . 



The time required for the passage of the lymph through the walls of the 

 capillaries of the abdomen or of the lower extremity, is about 2 minutes in the 

 dog; for the propulsion of the lymph through the lymphatics of the lower ex- 

 tremity and of the trunk, 3.2 seconds. 



The respiratory movements have an important influence upon the 

 lymph-stream in the thoracic duct and the right lymphatic duct, as each 

 inspiration conveys the current of lymph, together with venous blood, 

 to the heart, and as a result the tension in the thoracic duct may even 

 become negative. 



Lymph-hearts. The lymph-hearts containing valves found in some ani- 

 mals, particularly cold-blooded animals, are deserving of consideration. The frog 

 possesses two axillary hearts (above the shoulder near the vertebral column) 

 and two sacral hearts (above the anus near the apex of the sacrum) . They beat, 

 though not synchronously, about 60 times in the minute and contain about 10 

 cu. cm. of lymph. They contain striated muscle-fibers and are provided with 

 .special ganglia. The posterior hearts pump the lymph into the branches of the 

 communicating iliac vein, the anterior into the subscapular vein. 



Their pulsation depends in part on the spinal cord, for, as a rule rapid de- 

 struction of trie cord causes cessation of the heart-beat, but pulsations are not 

 rarely observed to continue after removal of the cord. A second normal source 



