MOVEMENTS OF THE LYMPH AND THE CHYLE 265 



in the intestine. Their constitution is not constant ; and they are com- 

 posed of the different varieties of fat taken as food, mixed in various 

 proportions. The ordinary corpuscular elements of the lymph are also 

 found in variable quantity in the chyle. 



MOVEMENTS OF THE LYMPH AND THE CHYLE 



Compared with the current of blood, the movements of the lymph 

 and chyle are feeble and irregular ; and the character of these move- 

 ments is such that they are evidently due to a variety of causes. As 

 regards constituents derived directly from the blood, the lymph may be 

 said to undergo a true circulation ; inasmuch as there is a constant 

 transudation at the peripheral portion of the vascular system, of liquids 

 that are returned to the circulating blood by the communications of the 

 lymphatic system with the great veins. The constituents of the lymph, 

 however, are not derived entirely from the blood, a considerable portion 

 resulting from interstitial absorption in the general lymphatic system ; 

 and the chyle contains certain nutritive matters absorbed by the lacteal 

 vessels. These are, physiologically, the most important constituents of 

 the lymph and chyle ; and they are taken up simply to be carried to the 

 blood and do not pass again from the general vascular system into the 

 lymphatics. 



So far as the mode of origin of the lymph and chyle has any bearing 

 on the movements of these liquids in the lymphatic vessels, there is no 

 difference between the imbibition of new matters from the tissues or 

 from the intestinal canal and the transudation of the liquid portions of 

 the blood ; for the mechanism of the passage of liquids from the blood- 

 vessels is such that the motive power of the blood can not be felt. An 

 illustration of this is in the mechanism of the production of the liquid 

 portions of the secretions. So far as the flow in the vessels of medium 

 size is concerned, the movement probably is continuous, subject only 

 to certain momentary obstructions or accelerations from various causes ; 

 but in the large vessels situated near the thorax and in those within the 

 chest, the movements are in a marked degree remittent, or they may 

 even be intermittent. All experimenters who have observed the flow of 

 lymph or chyle from a fistula in the thoracic duct have noted a constant 

 acceleration with each act of expiration ; and an impulse synchronous 

 with the pulsations of the heart has frequently been observed. 



The fact that the lymphatic system is never distended, and the ex- 

 istence of valves, by which different portions may become isolated, 

 render it impossible to estimate the general pressure in these vessels. 

 This undoubtedly is subject to great variations in the same vessels at 

 different times as well as in different parts of the lymphatic system. 



