44 HUMAN PHYSIOLOGY. 



layers of the mesentery. Chyle has a composition similar to that of lymph, 

 but it contains in addition, numerous fatty granules, each surrounded by an 

 albuminous envelope. When examined microscopically, the chyle presents 

 a fine molecular basis, made up of the finely divided granules of fat. 



COMPOSITION OF CHYLE. 



Water, 902.37 



Albumin, 35. 1 6 



Fibrin, 3.70 



Extractives, 15.65 



Fatty matters, . 36.01 



Salts 7.11 



1000.00 



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 lymphatic 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 muscular fibres within the walls 

 of the villus. At the time of contraction, the lymphatic capillary is com- 

 pressed and shortened, and its contents forced onward into the true lym- 

 phatic. When the muscular fibres relax, regurgitation is prevented by the 

 closure of the valve in the lymphatic at the base of the villus. 



As the walls of the lymphatic vessels contain muscular fibres, when they 

 become distended, these fibres contract and assist materially in the onward 

 movement 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 inspi- 

 ratory 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. 



