een finely
divided by pressing it through a piece of wire gauze. Also drop in a
single large lump. Keep in a warm place (about the temperature of the
body) for several hours or a day, examining from time to time. What is the
general effect of the artificial gastric juice upon the egg?

*To illustrate Effect of Alcohol upon Gastric Digestion.*--Prepare a
tumbler half full of artificial gastric juice as in the above experiment,
and add 10 cubic centimeters of this to each of six clean test tubes
bearing labels. To five of the tubes add alcohol from a burette as
follows: (1) .5 c.c., (2) 1 c.c., (3) 1.5 c.c., (4) 2 c.c., and (5) 3
c.c., leaving one tube without alcohol. Now add to each tube about 1/4
gram of finely divided white of egg from the experiment above, and place
all of the tubes in a beaker half full of water. Keep the water a little
above the temperature of the body for several hours, examining the tubes
at intervals to note the progress of digestion. Inferences.

CHAPTER XI - ABSORPTION, STORAGE, AND ASSIMILATION

The dissolved nutrients, to reach the cells, must be transferred from the
alimentary canal to the blood stream. This process is known as
_absorption_. In general, absorption means the penetration of a liquid
into the pores of a solid, and takes place according to the simple laws of
molecular movements. The absorption of food is, however, not a simple
process, and the passage takes place through an _active_ (living)
membrane. Another difference is that certain foods undergo chemical change
while being absorbed.

*Small Intestine as an Organ of Absorption.*--While absorption may occur to
a greater or less extent along the entire length of the alimentary canal,
most of it takes place at the small intestine. Its great length, its small
diameter, and its numerous blood vessels all adapt the small intestine to
the work of absorption. The transverse folds in the mucous membrane, by
retarding the food in its passage and by increasing the absorbing surface,
also aid in the process. But of greatest importance are the minute
elevations that cover the surface of the mucous membrane, known as

*The Villi.*--Each single elevation, or villus, has a length of about one
fiftieth of an inch and a diameter about half as great (_A_, Fig. 76), and
contains the following essential parts:

1. An outer layer of epithelial cells, resting upon a connective tissue
support.

2. A small lymph tube, called a _lactea