572 



Anatomy, Physiology, and Pathology of the 



conveyed into the general circulation, while the effete matter is 

 passed onwards in the canal to be expelled from the system. 



The vessels which transmit the chyle are designated the lac- 

 teals ; and as its entrance into them is one of the most interest- 

 ing and instructive phenomena in the animal economy, we shall 

 describe it somewhat at length. The absorption of chyle taking 

 place in the small intestines, the lacteals are freely distributed 

 here, and consequently a different development of their internal 

 lining membrane exists compared with that of the large intestines. 

 In the former it is thickly studded with shaggy projections, villi ; 

 hence the name, the villous or velvety tunic. Each villus is plen- 

 tifully supplied with blood-vessels, besides which it contains 

 nerves and the radicles of the lacteal absorbents. The minute- 

 ness of these tubes, added to other physical causes, has however 

 prevented their precise arrangement being demonstrated ; but it is 

 generally believed that they are formed into 

 loops more or less perfect, as shown in the 

 annexed diagram.* The several component 

 parts of a villus are united together by areolar 

 tissue, and are protected by a scaly epithelial 

 covering. This epithelium is a membrane 

 analogous to the cuticle of the true skin, and 

 is formed after a like manner, and performs 

 a similar office by defending the sensible struc- 

 tures beneath it from injury. By some phy- 

 siologists the epithelium is supposed to be 

 cast off from the surface of the villi during the activity of chylifi- 

 cation and absorption, and to be reproduced in the intervals of 

 their suspension ; by others however this shedding is not regarded 

 as an essential step in either process. Immediately beneath the 

 epithelial scales lies a great number of cells varying in size from 

 the -roV o- to the -g-oVo of an inch, whose office it is to imbibe the 

 chyle and transmit it to the radicles of the lacteals. The trans- 

 mission of the chyle to these minute tubes is effected by the 

 bursting or deliquescence of the cells after acquiring their full 

 size ; but its entrance into them is due to the law of endosmose 

 and exosmose. The imbibition, however, of chyle alone by the 

 cells, as they are surrounded by other matters, some of which are 

 even necessary to the well-being of the various organs, shows a 

 power of selection by them, which doubtless is an act of vitality. 



We cannot now speak of the means provided for a constant deve- 

 lopment of new cells ; but it is right to add a few words on endos- 

 mose and exosmose, and which we prefer to do in the appropriate 

 language of Dr. Carpenter. He says, that " when two fluids 



* -From Kii'kes and Paget's ' Handbook of Physiology.' 



