CHAPTER V.

SECRETION.

1. THE word secretion means a separation of fluids. When it is used in physiology, it has reference to a certain process by which various substances are separated from the blood, without being changed in their separation. We call this act of separation secretion; and we also call the substance that is separated secretion; as we say that by secretion the gastric juice is formed in the stomach, and we say also that the gastric juice is a secretion of the stomach. Both are correct.

2. Without secretion there would be no possible way for the different parts of the body to be nourished, and many injurious substances would not be discharged from the blood; therefore it is very important for our health that these secretions should not be interrupted. These substances, though derived and separated from the blood, are very different in appearance and composition from the blood, as we shall see.

3. There are three kinds of organs for the purpose of secretion, which I wish you to remember, when I have explained them to you.

First-THE EXHALANT VESSELS.

What is the subject of chapter fifth? 1. What does secretion mean? How is the term used in physiology? What two things does this word comprehend? What is an example? 2. What are the advantages of secretion? How important is secretion to health? Are the secreted substances similar to the blood? 3. How many kinds of secretory organs are there? What is the first kind?

FAT SYNOVIA-MARROW.

Second-THe follicles.

Third-THE glands.

73

4. You may recollect that I have informed you that there are a great many little vessels through which the chyle passes over the intestines. These are called capillaries, and it is thought by many that the exhalant vessels, which are very small, are connected with them. These exhalations are internal, when they take place in the body. The head, chest, and stomach are all lined with a thin covering, which throws out a little fluid, sufficient to keep them moist, and enable them to move easily.

5. The fat, of which I have heretofore spoken, is caused by exhalation, or is one form of secretion. It is first an oily, greasy fluid, then becomes hard, and serves as a protection to the skin. Then the ligaments around the joints are lined with the same kind of membrane as the stomach; this secretes the synovia, which enables the joints to move easily.

6. The marrow that is in the long bones is another secreted exhalation. The use of the marrow is not known. Many supposed it were to make the bones less liable to be broken; but there is more of it in the bones of aged than in those of younger persons, and their bones are much more easily broken.

7. The external exhalations are those which take place out of the body. These are the sweat or perspi

3. What is the second kind? What is the third kind? 4. With what are the exhalant vessels connected? What is meant by internal exhalations? Where are some of the internal exhalations found? 5. By what is the fat caused? How is it formed? What is the synovia, and where is it secreted? 6. What secretion is contained in the long bones? What is the use of the marrow? How do we know that it does not strengthen the bones? 7. What is meant by external exhalations?

ration that is continually passing off, and a little mist or fluid which passes from the lungs.

FOLLICLES.

8. The second division of secretory organs is called These are little bags, found in the skin near the surface. They secrete an oily substance. When this does not pass through the pores of the skin, it appears like a little ridge or worm; but if the pores be kept open by frequent bathing, this fluid will pass off as soon as it is secreted. There are follicles in each ear to secrete the ear-wax, which will produce deafness if it be not removed. There is a little follicle at the root of each hair; and the difference between the moistness in the hair of different persons depends on the amount of liquid that the follicle secretes.

9. The third division of secretory organs is called glands. These are situated in different parts of the

8. What is the second

7. What are some of the external exhalations? division of secretory organs? What are the follicles? How does their secretion appear? What is necessary for us to do that this secretion may pass off? What does the follicle in the ear secrete? What is one cause of deafness? What is the use of the follicle at the root of the hair? 9. What is the third division of secretory organs ?

body, and are of various sizes; some being quite small, others quite large, weighing several pounds, and contain arteries and veins to carry the blood to them and return it again. The substances which the glands secrete differ very much in appearance from the blood, although they are formed from it.

10. It is thought that the elements of all the different secretions exist in the blood; but when different elements are united in different quantities or proportions, the result, of course, is different; for the same reason that a certain quantity of oxygen gas, being united with several different gases, makes air; but if we unite another quantity of the same oxygen gas with other gases, it makes water; so that if two or more elements existing in the blood were united, they would produce tears; while several other elements would make the gastric juice, and so on with all the other secretions.

11. There is, however, a principle of life within us, that regulates all these different operations, that they may produce the desired result. Some of the most important fluids which the glands secrete, are the following: first, the

SALIVA.

12. The saliva is formed by three pairs of glands, situated in the mouth. They secrete the fluid which passes into the mouth through a little tube in the muscles of the face. Its principal use when mixed with the

9. Describe the glands. Are the substances secreted by the glands similar to the blood? 10. Are these substances contained in the blood? What produces the difference between them? Explain in what way this principle holds true in reference to different quantities of the same gas? 11, What regulates all these different operations? What is the first fluid that is secreted by the glands? 12. How is the saliva formed? How does pass into the mouth?

it

food, is to moisten it, and render its passage more easy down the throat. It also makes the voice clearer and better, by keeping it moist. The saliva has no smell, taste, or color, is a little heavier than water, and contains some salt and a little acid.

GASTRIC JUICE.

13. This fluid is secreted in the stomach, and very much resembles the saliva; yet it is more powerful in its operations, and of more importance to us in its use. During the process of digestion, this fluid is poured on the food, and dissolves it into a soft mass, which is called chyme. It has the same effect on the food that rennet has on milk in the process of making cheese. So when little infants throw up their milk from their stomachs in a curdled state, it shows that their stomachs are in a healthy condition.

14. It is nearly tasteless, and without odor, yet it has the quality of preventing putrefaction, and will even remove it after it has commenced. It is said that portions of dead bodies, which become putrid and disagreeable, when taken into the stomachs of some animals, become perfectly inoffensive, and as in a state of preservation.

15. Though the gastric juice possesses those remarkable solvent properties, which enable it to dissolve even the hardest substances, yet it has no power to act on

12. What is its principal use? What are the properties of the saliva? 13. What is the second secretion of the glands? Where is the gastric juice secreted? In what does it differ from the saliva? What is its use? What effect has it on our food? When do we judge that the stomach of infants are in a healthy condition? 14. What are the principal properties of the gastric juice? 15. Does the gastric juice act on substances having life?