INTRODUCTION OF FAT. 91 



taculum chyli, several lymphatic trunks opening into it ; 13, the thoracic 

 duct, dividing opposite the middle of the dorsal vertebra? into two branch- 

 es, which soon reunite ; the course of the duct behind the arch of the 

 aorta and left subclavian artery is shown by a dotted line ; 14, the duct, 

 making its turn at the root of the neck, and receiving several lymphatic 

 trunks previously to terminating in the posterior aspect of the junction 

 of the internal jugular and subclavian vein ; 15, the termination of the 

 trunk of the ductus lymphaticus dexter. 



As to the manner in which digested fat finds its way into the lacteals, 

 it seems to be as follows: In the interior of the epithelial Mannerofthe 

 cells oil-drops are detected, while on the outer part the sur- introduction of 

 face presents a pearly aspect, from other portions of oil wait- fat ' 

 ing to enter. By degrees, all the cells upon the exterior of the villus ex- 

 hibit the same appearance, the particles gradually finding their way 

 through the parenchyma of the villus, and so entering the lacteal tube. 

 If, with some anatomists, we regard the lacteal at its origin as not being 

 a true vessel, but only an excavation in that parenchyma, much of the 

 obscurity which surrounds the explanation of the manner of the entry 

 of oleaginous material into the lacteal is removed. If, moreover, with 

 other anatomists, we represent the intestinal end of the cylindric cells to 

 be wanting, and the cells themselves to be truly cup-shaped forms, filled 

 with a peculiar secretion, through which fat particles and even solid sub- 

 stances may pierce their way, this likewise would remove much of the 

 difficulty. But, after all, even if the general opinion of the structure of 

 a villus is adopted, that the lacteal commences with a blind pouch or 

 blunt tube surrounded by a network of blood-vessels, and over this an 

 epithelium cast, there being no mouths, or pores, or apertures of discov- 

 erable size leading into the lacteal through its own wall and enveloping 

 structures, we should also remember the extreme minuteness of the oily 

 particles suspended in the chyle, and still more particularly that even 

 this size, small as it is, is deceptive ; for, in passing through interstices 

 too minute to be seen even by optical aid, the oil particles may be press- 

 ed out into long, thread-like forms, which, as soon as they escape into the 

 free cavity of the lacteal, assume the spheroidal appearance by reason of 

 their own cohesion, just as a blood-cell can pass through a vessel of a 

 diameter far less than its own by lengthening itself out into a linear 

 shape, and reassuming its original figure as soon as it escapes from con- 

 finement and pressure. Though, therefore, the lacteals commence upon 

 the intestinal walls as closed tubes, this, in reality, offers no obstacle to 

 their absorbing power when their molecular porosity is considered. 



Perhaps this infiltration or intrusion of oily material is, to a consid- 

 erable extent, aided by the presence of the bile, or, rather, its oily con- 

 stituent. It is capable of easy demonstration that oil will rise much 



