THE ABSORBENT SYSTEM 427 



the body and becoming first assimilated to and then incorporated 

 with it. 



The process by which the solutions of sugar, oil, proteids, or salts 

 penetrate the wall of the alimentary tract is termed "osmosis", and can 

 easily be shown by immersing a bladder filled with thick syrup in a 

 jar of pure water, when a double current is immediately established. 

 Some of the sugar solution escapes into the surrounding water, whilst 

 a much larger proportion of pure water passing through the membrane 

 to the syrup enters the bladder, dis- 

 tending it to the utmost and even to 

 bursting. 



The lacteal system may be said to 

 commence in the delicate velvet pile- 

 like processes or villi which line the 

 whole of the small intestine, and which 

 are shown in the accompanying wood- 

 cut (fig. 182, 1). 



Each villus contains a net-work of 

 minute blood-vessels, not here de- 

 picted, surrounding a vessel of larger 

 size (2), which is the lacteal. The 

 latter, commencing near the summit 

 in a blind extremity or a loop, passes 

 down to the base of the villus, where 

 it joins with others to form a net- work. 

 These, after meeting together, emerge 

 from the intestine as vessels of con- 

 siderable size (2, 2), which accompany 

 the blood-vessels of the mesentery, and, gradually uniting to form larger 

 and larger trunks, terminate beneath the spine in a kind of sac or 

 bladder (receptaculum chyli) which represents the hinder end of the 

 thoracic duct. Whilst still contained within the villi, the lacteals are 

 surrounded by muscular fibres, and when these fibres contract, the villi 

 are changed in form from long finger-like processes into short projections, 

 and the fluid they have absorbed, to which the term chyle (Greek chulos, 

 juice) is applied, is consequently driven into the underlying net- work of 

 vessels. The villi thus constitute small force-pumps which, though in- 

 dividually feeble, yet as a result of their numbers become important agents 

 in the onward movement of the lacteal fluid. The vessels forming the 

 net-work are provided with valves in their course which do not allow any 

 backward current, but compel the fluid absorbed to move on towards the 



Fig. 182. Section through the Small Intestine 



1 Villi. 2 Lacteal Vessels. Muscular Coat. 

 4 Serous Coat. 



