s urea--an interference which in some instances
results in great harm. It has also been shown that malted liquors, such as
beer and ale, contain substances which, like the caffein of tea and coffee
(page 167), are readily converted into uric acid.(76) Wines contain acids
which may also act injuriously. The harm which such substances do is, of
course, additional to that caused by the alcohol.

*Summary.*--As a result of the oxidations and other changes at the cells,
substances are produced that can no longer serve a purpose in the body.
They are of the nature of waste, and their continuous removal from the
body is as necessary to the maintenance of life as the introduction of
food and oxygen. The organs whose work it is to remove the waste,
excepting the lungs, are glands; and the material which they remove are of
the nature of secretions. From the cells, the waste passes through the
lymph in the blood. From the blood it is separated by the excretory organs
and passed to the exterior of the body.

*Exercises.*--1. What general purposes are served by the glands in the
body?

2. What are the parts common to all glands? What purpose is served by each
of these parts?

3. How do tubular glands differ in structure from saccular glands? What is
a racemose gland? Why so called?

4. Describe the nature of the secretory process.

5. What conditions render necessary the formation of waste materials in
the body? Why must these be removed?

6. How do the waste materials get from the cells to the organs of
excretion?

7. Show by a drawing the connections of the kidneys with the large blood
vessels and the bladder. Name parts of drawing.

8. In what do the uriniferous tubes have their beginning? In what do they
terminate? With what are they lined?

9. Why should the blood pass through two sets of capillaries in the
kidneys?

10. Bright's disease of the kidneys affects the uriniferous tubes and
interferes with their work. What impurity is then left in the blood?

11. Trace water and salts from the Malpighian capsules to the bladder,
naming parts through which they pass.

12. Trace carbon dioxide from the cells to the outside atmosphere.

13. How does the quantity of material introduced into the body compare
with that which is removed by the organs of excretion?

14. Name two ways of lessening the work of the kidneys.

15. Why is the drinking of plenty of pure water a healthful practice?

PRACTICAL WORK

*To