CARPENTER, ON HUMAN PHYSIOLOGY. 285 
and the formation of peptones and parapeptones by Meissner, 
are given in detail. A great deal has been recently done 
with regard to the nature and action of the pancreatic juice 
and the bile, and the sections devoted to these subjects 
are full of new and interesting matter. There is an inte- 
resting account of the structure of the villi, and as this 
subject is entirely microscopical, we are induced to give an 
extract from this part of the work to show, in the first place, 
how well the editor has kept up with his time, and, in the 
second place, to show in what a bold and instructive manner 
microscopic illustrations may be produced in wood. 
106. The villi are extensions of the mucous lining of the intes- 
tinal canal, which thickly beset its surface from the pyloric orifice 
to the cecum, that is, through the entire 
Fig. 18 length of the small intestine, to which 
rm they are limited in man. They have 
usually somewhat the form of the finger 
of a glove, being sometimes nearly cylin- 
drical sometimes rather conical, whilst 
they not unfrequently become  flat- 
tened and extended at the base, so that 
two or more coalesce. Their length varies 
from 1-4th to 1-3rd of a line, or even more; 
and the broad flattened kinds are about 
1-6th to 1-8th of a line in breadth. In 
the upper part of the small intestine, 
where they are most numerous, it has 
been calculated by Krause that there are 
not less than from 50 to 90 in a square 
line; and in the lower part, from 40 to 70 
in the same area. The details of their 
structure are of extreme interest in re- 
or _ _.. ference to the mechanism of absorption. 
ve hele liens Gitok ™ Tf the plan pursued by Teichmann, that of 
injection, be adopted, the appearances pre- 
sented are those shown in Figs. 19, 20, and 21, taken from the 
beautiful plates which accompany his work on the Lymphatic 
System.* From these it appears that the lacteals commence either 
by a simple closed extremity, or by a loop, though in broad villi 
a network is sometimes visible. The tube or tubes occupying the 
centre of the villus appear to possess perfectly definite walls, and 
are larger than the numerous capillary blood-vessels which surround 
and are external to them. ‘Their average diameter is about 
1-800th or 1-1000th of an inch; but they present here and there 
slight dilatations and contractions, and at the base of the villus 
terminate in a network of lacteal vessels immediately subjacent 
to the Lieberkiihnian follicles (Fig. 206), termed by Teichmann, 
from the closeness of the meshes, the Reta angustum. This plexus 
communicates with another possessing larger vessels, which are sup- 
plied with valves, are more deeply situated in the submucous areolar 
* Ludwig Teichmann, ‘ Das Saugader System,’ Leipzig, 1861. 
