110 HUMAN PHYSIOLOGY. , 



Forces Aiding the Movement of Lymph and Chyle. The lymph and 

 chyle are continually moving in a progressive manner from the periphery or 

 beginning of the lymphatic system to the final termination of the thoracic 

 duct. The force which primarily determines the movement of the lymph 

 has its origin in the beginnings of the lymph-vessels, and depends upon the 

 difference in pressure here and the pressure in the thoracic duct. The greater 

 the quantity of fluid poured into the lymph-spaces, the greater will be the 

 pressure and, consequently, the movement. The first movement of chyle 

 is the result of a contraction of the muscle-fibers within the walls of the villus. 

 At the time of contraction the lymph capillary is compressed and shortened, 

 and its contents are forced onward into the true lymphatic. When the 

 muscle-fibers relax, regurgitation is prevented by the closure of the valve in 

 the lymphatic at the base of the villus. 



As the walls of the lymph vessels contain muscle-fibers, when they become 

 distended these fibers contract and assist materially in the onward move- 

 ment of the fluid. 



The contraction of the general muscular masses in all parts of the body, 

 by exerting an intermittent pressure upon the lymphatics, also hastens the 

 current onward; regurgitation is prevented by the closure of valves which 

 everywhere line the interior of the vessels. 



The respiratory movements aid the general flow of both lymph and chyle 

 from the thoracic duct into the venous blood. During the time of an in- 

 spiratory movement the pressure within the thorax, but outside the lungs, 

 undergoes a diminution in proportion to the extent of the movement; as a 

 result, the fluid in the thoracic duct outside of the thorax, being under a 

 higher pressure, flows more rapidly into the venous system. At the time of 

 an expiration, the pressure rises and the flow is temporarily impeded, only to 

 begin again at the next inspiration. 



BLOOD. 



The blood is a nutritive fluid containing all the elements necessary for the 

 repair of the tissues; it also contains principles of waste absorbed from the 

 tissues, which are conveyed to the various excretory organs and by them 

 eliminated from the body. 



The total amount of blood in the body is estimated to be about one nineteenth 

 of the body-weight; from six to eight pounds in an individual of average 

 physical development. The quantity varies during the twenty-four hours, 

 the maximum being reached in the afternoon, the minimum in the early 

 morning hours. 



