Fig. no. The Tho- 

 racic Duct. 



i, the thoracic duct, in 

 front of the vertebral 

 column ; its upper ex- 

 tremity communicating 

 with the venous system 

 at the junction of the 

 left jugular and left sub- 

 clavian veins (compare 

 with fig. 6) ; 2, recep- 

 taculum chyli ; 3, in- 

 ferior vena cava, lower 

 portion ; 4, superior 

 vena cava. 



ABSORPTION 1 1 5 



digested food- sub stances, only an extremely 

 thin layer of tissue separating. Hence in 

 the villi absorption goes on very rapidly, 

 both by the blood-vessels and the lacteals. 

 This is also supplemented by means of 

 other blood-vessels and lacteals which lie 

 in the mucous membrane between the villi, 

 and also in the corresponding membrane 

 of the large intestine where there are no 

 villi. 



The absorption as carried on by the lac- 

 teals differs in one important respect from 

 that by the blood-vessels, since the former 

 have the power to select the fatty constitu- 

 ents from the various products of digestion, 

 while the latter possess no power of selection. 



During fasting the lacteals contain a clear, 

 transparent fluid, closely resembling that 

 which fills the other lymphatic capillaries ; but 

 during digestion they contain a milky fluid 

 called chyle (Gr. chulos> juice), the change in 

 appearance being due to the innumerable 

 particles of fatty matter absorbed from the 

 intestine. 



The chyle is collected by lymphatic 

 vessels, which resemble thin- walled veins (see 

 page 131). Like veins, they are also provided 

 with valves which allow of the passage of 

 fluid in one direction only, viz. towards the 

 thoracic duct ; and the valves are arranged 

 at such short distances from each other, that, 

 when full, the lymph-vessels have a knotted 

 or beaded appearance. 



As the chyle moves onward, and especially 

 as it passes through the lymphatic glands, 

 the number of oily particles diminishes, cor- 

 puscles resembling the white corpuscles of 

 the blood (see page 117), and a nitrogenous 

 substance called fibrin are formed : in fact, 

 as it approaches the blood system which it 

 is ultimately to enter, it becomes more and 

 more like blood, excepting in the matter of 

 red corpuscles which give the colour. We 

 may .therefore regard the lymphatic glands 

 as being concerned in the elaboration of the 

 blood. 



IP! 



