28 THE FUNCTIONS OF ANIMALS. 
said to have slight power of converting starch into sugar; by its 
alkalinity it helps the action of the trypsin of the pancreas (which, 
unlike pepsin, acts in an alkaline fluid) ; it affects cell membranes, so 
that they allow the passage of small drops of fat and oil; and it is said 
to have various other qualities. 
(e) In addition to the liver and the pancreas, there are on the walls 
of the small intestine a great number of small glands, which secrete a 
juice which seconds the pancreatic juice. The digested material is 
in part absorbed into the blood, and the mass of food, still being 
digested, is passed along the small intestine by means of the muscular 
contraction of the walls known as peristaltic action. It reaches the 
large intestine, and its reaction is now distinctly acid by reason of 
the acid fermentation of the contents. The walls of the large intestine 
contain glands similar to those of the small intestine, and the digestive 
processes are completed, while absorption of water also goes on; so 
that by the time the mass has reached the rectum, it is semi-solid, 
and is known as feeces. These contain the indigestible and un- 
digested remnants of the food and the useless products of the chemical 
digestive processes. 
Absorption.— But the food must not only be rendered 
soluble and diffusible, it must be carried to the different 
parts of the body, and there incorporated into the hungry 
cells. It is carried by the blood stream, and in part also 
by what are called lymph vessels, which contain a clear 
fluid resembling blood mus red blood corpuscles. 
Absorption begins in the stomach by direct osmosis into the capillaries 
or fine branches of blood vessels in its walls, and_a similar absorption, 
especially of water, takes place along the whole of the digestive tract. 
But lining the intestines there are delicate projections called villi; 
they contain capillaries belonging to the portal system (blood vessels 
going to the liver), and small vessels known as lacteals connected 
with lymph spaces in the wall of the intestine. The lacteals lead into 
a longitudinal lymph vessel or thoracic duct, which opens into the 
junction of the left jugular and left subclavian veins at the root‘of the 
neck. The contents of the duct in a fasting animal are clear; after a 
meal they become milky ; the change is due to the matters discharged 
into it by the lacteals. It is probable that nearly all the fat of a meal 
is absorbed from the intestines by the lacteals, but it is not certain in 
what measure, if at all, this is true of the other dissolved foodstuffs ; 
the greater part certainly passes into the capillaries of the portal 
system, which are contained in the villi. The digested proteid, 
chiefly in the form of amino-acids, passes into the blood of the portal 
vein, either directly or through the intermediary of leucocytes, which 
flock to the intestine when proteid food is being digested. 
Function of the liver—We now know the fate of the 
fats, and of the proteids of the food, and the manner in 
