374 



MANUAL OF HISTOLOGY. 



Fig. 371. Villus from the intestine of a kid, 

 after treatment with acetic acid. 



portion of the system presiding over the absorption of the chyle is, how- 

 ever, on account of its dark fatty contents during digestion, more favour- 

 able for observation, and was in fact 

 the only point, a few years ago, at 

 which the relations of the vessels in 

 question could be studied with any 

 success. 



In the first place, then, let us take 

 a glance at the lacteals. 



If we choose for examination the 

 intestinal villi of a mammal which 

 has been fed some hours before with 

 rich fatty food, such as that of a young 

 sucking animal. (fig. 371), which best 

 answers our purpose, we shall see, in 

 the central portion of eachvillus travers- 

 ing its axis, a passage filled with 

 minute fatty molecules, and dark on 

 that account. This duct frequently 

 terminates in a rounded enlargement or bulb, and is usually single in 

 slender villi, although in instances in which the latter are broader it 

 has been seen to be double, treble, or quadruple. 



Minutely examined, this vessel (fig. 372, d), which has a diameter of 

 0'0187-0*982 mm., is seen to possess a thin 

 homogeneous, but distinct wall. Above, it ter- 

 minates blind, without the interposition of any 

 finer system of canals, and may be expanded at 

 its end to a diameter of O'OSOO mm. in some 

 cases. This axial vessel has been supposed by 

 some to be merely a deficiency in the connective- 

 tissue substance of the villus, but this is incor- 

 rect. Years ago I had frequently met with the 

 villus half torn through, and the uninjured wall 

 of the axial canal thus isolated. The results of 

 artificial injection ( 208) have since corrobo- 

 rated this explanation of its nature. Around 

 this chyle radicle the capillaries of the loop net- 

 work (b), mentioned in section 205, are coiled 

 with a thin layer of unstriped muscle-cells inter- 

 posed : a fact of great interest. 



Lymphatic radicles were observed also, many 

 years ago, by Koettiker in the tail of the tadpole. 

 Their appearance as they occur here is very 

 variable. They most usually present themselves, 

 however, in the form of tubes much finer than 

 in the preceding case, measuring in diameter 

 0'0045-0'0113 mm., and consisting of a thin 

 homogeneous wall, which is nucleated and stud- 



372. Intestinal villus. o, 

 the thick border of the cylin- 

 der epithelium; 6, capillary 

 network ; c, longitudinally ar- 

 ranged smooth muscle fibres; 

 rf, chyle radicle in the axis. 



ded with a multitude of minute saccules. 



They are arranged as a whole in the form of a tree, with branches passing 

 off at acute angles, and do not present the reticulated appearance of the blood 

 capillaries. The terminal tubules seem to end in delicate filiform processes, 

 directed towards similar ramifications belonging to stellate formative cells. 



