CIRCULATING SYSTEM. 337 
The structure of the lacteal and lymphatic vessels 1s si- 
milar. They are composed of two coats, an internal and 
external, the former being thin and smooth, the latter fibrous. 
The extent of the absorbing power, however, is not the same 
in both. ‘The lacteals appear to be incapable of absorbing 
any thing else but chyle. M. Macenpt *, administered to 
a dog diluted alcohol during digestion; and, although he 
was able to detect its presence in the blood, yet in the chyle 
no traces of it could be perceived. The experiments of Sir 
E. Home, already quoted, and which have been repeated 
by M. Macenor fF, (in reference to the use of the spleen,) 
lead to the same results. The absorbing power of the | ym- 
phaties is not so limited. Dispersed throughout the whole 
body, and destined to absorb occasionally every substance 
of which it consists,—fat, bone, the watery part of the bile, 
urine, and feeces, when too long retained,—they are like- 
wise capable of taking up a variety of foreign substances, 
when brought into contact with the orifices of their roots. 
It is owmg to the action of the lymphatics, that alcohol, 
camphor, rhubarb, and a variety of other substances thrown 
imto the stomach, which the lacteals do not absorb, and 
different substances rubbed on the skin, are conveyed into 
the system. Attempts have been made to establish the 
opinion, that absorption of foreign matter takes place inde- 
pendent of either lacteals or lymphatics, since the blood 
exhibits proofs of the entrance of such into the system, which 
are not afforded by the contents of the thoracic duct. But 
the connection which has been pointed out between the lac- 
teal and’ lymphatic vessels and the veins, independent of 
the thoracic duct, throws a considerable degree of doubt 
over the supposition. 
The lacteals and lymphatics have been lone known as the 
absorbents in the mammalia. Huvwnrex, Hewson, and 

* Précis Elementaire de Physiologie, vol. ii. p. 168. + Ibid. p. 182. 
VOL. si. y 
