leaving the cells add to its bulk. These mix with the plasma from
the blood, forming the resultant liquid which is the lymph. A considerable
amount of the material absorbed from the food canal also enters the lymph
tubes, but this passes into the blood before reaching the cells.

*Composition and Physical Properties of the Lymph.*(26)--As would naturally
be expected, the composition of the lymph is similar to that of the blood.
In fact, nearly all the important constituents of the blood are found in
the lymph, but in different proportions. Food materials for the cells are
present in smaller amounts than in the blood, while impurities from the
cells are in larger amounts. As a rule the red corpuscles are absent from
the lymph, but the white corpuscles are present and in about the same
numbers as in the blood.

The physical properties of the lymph are also similar to those of the
blood. Like the blood, the lymph is denser than water and also coagulates,
but it coagulates more slowly than does the blood. The most noticeable
difference between these liquids is that of color, the lymph being
colorless. This is due to the absence of red corpuscles. The quantity of
lymph is estimated to be considerably greater than that of the blood.

*Lymph Vessels.*--Most of the lymph lies in minute cavities surrounding the
cells and in close relations with the capillaries (Figs. 27 and 30). These
are called _lymph spaces_. Connecting with the lymph spaces on the one
hand, and with certain blood vessels on the other, is a system of tubes
that return the lymph to the blood stream. The smallest of these, and the
ones in greatest abundance, are called _lymphatics_. They consist of
slender, thin-walled tubes, which resemble veins in structure, and, like
the veins, have valves. They differ from veins, however, in being more
uniform in size and in having thinner walls.

[Fig. 28]

Fig. 28--*Diagram of drainage system for the lymph.* 1. Thoracic duct. 2.
Right lymphatic duct. 3. Left subclavian vein. 4. Right subclavian vein.
5. Superior vena cava. 6. Lacteals. 7. Lymphatic glands. The small tubes
connecting with the lymph spaces in all parts of the body are the
lymphatics.

The lymphatics in different places gradually converge toward, and empty
into, the two main lymph tubes of the body. The smaller of these tubes,
called the _right lymphatic duct_, receives the lymph f