13. Give general directions for applying artificial respiration.

PRACTICAL WORK

Examine a dissectible model of the chest and its contents (Fig. 49). Note the relative size of the two lungs and their position with reference to the heart and diaphragm. Compare the side to side and vertical diameters of the cavity. Trace the air tubes from the trachea to their smallest divisions.

*Observation of Lungs* (Optional).-Secure from a butcher the lungs of a sheep, calf, or hog. The windpipe and heart should be left attached and the specimen kept in a moist condition until used. Demonstrate the trachea, bronchi, and the bronchial tubes, and the general arrangement of pulmonary arteries and veins. Examine the pleura and show lightness of lung tissue by floating a piece on water.

*To show the Changes that Air undergoes in the Lungs.*-1. Fill a quart jar even full of water. Place a piece of cardboard over its mouth and invert, without spilling, in a pan of water. Inserting a tube under the jar, blow into it air that has been held as long as possible in the lungs. When filled with air, remove the jar from the pan, keeping the top well covered. Slipping the cover slightly to one side, insert a burning splinter and observe that the flame is extinguished. This proves the absence of sufficient oxygen to support combustion. Pour in a little limewater(43) and shake to mix with the air. The change of the limewater to a milky white color proves the presence of carbon dioxide.

[Fig. 50]

Fig. 50-*Apparatus* for showing changes which air undergoes while in the lungs.

2. The effects ill.u.s.trated in experiment 1 may be shown in a somewhat more striking manner as follows: Fill two bottles of the same size each one fourth full of limewater and fit each with a two-holed rubber stopper (Fig. 50). Fit into each stopper one short and one long gla.s.s tube, the long tube extending below the limewater. Connect the short tube of one bottle and the long tube of the other bottle with a Y-tube. Now breathe slowly three or four times through the Y-tube. It will be found that the inspired air pa.s.ses through one bottle and the expired air through the other. Compare the effect upon the limewater in the two bottles. Insert a small burning splinter into the top of each bottle and note result. What differences between inspired and expired air are thus shown?

3. Blow the breath against a cold window pane. Note and account for the collection of moisture.

4. Note the temperature of the room as shown by a thermometer. Now breathe several times upon the bulb, noting the rise in the mercury. What does this experiment show the body to be losing through the breath?

*To show Changes in the Thoracic Cavity.*-1. To a yard- or meter-stick, attach two vertical strips, each about eight inches long, as shown in Fig.

51. The piece at the end should be secured firmly in place by screws or nails. The other should be movable. With this contrivance measure the sideward and forward expansion of a boy's thorax. Take the diameter first during a complete inspiration and then during a complete expiration, reading the difference. Compare the forward with the sideward expansion.

[Fig. 51]

Fig. 51-*Apparatus* for measuring chest expansion.

2. With a tape-line take the circ.u.mference of the chest when all the air possible has been expelled from the lungs. Take it again when the lungs have been fully inflated. The difference is now read as the chest expansion.

[Fig. 52]

Fig. 52-*Simple apparatus* for ill.u.s.trating the action of the diaphragm.

*To ill.u.s.trate the Action of the Diaphragm.*-Remove the bottom from a large bottle having a small neck. (Scratch a deep mark with a file and hold on the end of this mark a hot poker. When the gla.s.s cracks, lead the crack around the bottle by heating about one half inch in advance of it.) Place the bottle in a large gla.s.s jar filled two thirds full of water (Fig. 52). Let the s.p.a.ce above the water represent the chest cavity and the water surface represent the diaphragm. Raise the bottle, noting that the water falls, thereby increasing the s.p.a.ce and causing air to enter.

Then lower the bottle, noting the opposite effect. To show the movement of the air in and out of the bottle, hold with the hand (or arrange a support for) a burning splinter over the mouth of the bottle.

*To estimate the Capacity of the Lungs.*-Breathing as naturally as possible, expel the air into a spirometer (lung tester) during a period, say of ten respirations (Fig. 53). Note the total amount of air exhaled and the number of "breaths" and calculate the amount of air exhaled at each breath. This is called the _tidal_ air.

[Fig. 53]

Fig. 53-*Apparatus* (spirometer) for measuring the capacity of the lungs.

2. After an ordinary inspiration empty the lungs as completely as possible into the spirometer, noting the quant.i.ty exhaled. This amount, less the tidal air, is known as the _reserve_ air. The air which is now left in the lungs is called the _residual_ air. On the theory that this is equal in amount to the reserve air, calculate the capacity of the lungs in an ordinary inspiration.

3. Now fill the lungs to the full expansion of the chest and empty them as completely as possible into the spirometer, noting the amount expelled.

This, less the tidal air and the reserve air, is called the _complemental_ air. Now calculate the total capacity of the lungs.

CHAPTER VIII - Pa.s.sAGE OF OXYGEN THROUGH THE BODY

What is the nature of oxygen? What is its purpose in the body and how does it serve this purpose? How is the blood able to take it up at the lungs and give it off at the cells? What becomes of it after being used? These are questions touching the maintenance of life and they deserve careful consideration.

*Nature of Oxygen.*-To understand the relation which oxygen sustains to the body we must acquaint ourselves with certain of its chemical properties. It is an element(44) of intense affinity, or combining power, and is one of the most active of all chemical agents. It is able to combine with most of the other elements to form chemical compounds. A familiar example of its combining action is found in ordinary combustion, or burning. On account of the part it plays in this process, oxygen is called the _supporter of combustion_; but it supports combustion by the simple method of uniting. The ashes that are left and the invisible gases that escape into the atmosphere are the compounds formed by the uniting process. It thus appears that oxygen, in common with the other elements, may exist in either of two forms:

1. That in which it is in a _free_, or uncombined, condition-the form in which it exists in the atmosphere.

2. That in which it is a part of compounds, such as the compounds formed in combustion.

Oxygen manifests its activity to the best advantage when it is in a free state, or, more accurately speaking, when it is pa.s.sing from the free state into one of combination. It is separated from its compounds and brought again into a free state by overcoming with heat, or some other force, the affinity which causes it to unite.

*How Oxygen unites.*-The chemist believes oxygen, as well as all other substances, to be made up of exceedingly small particles, called _atoms_.

The atoms do not exist singly in either elements or compounds, but are united with each other to form groups of atoms that are called _molecules_. In an element the molecules are made up of one kind of atoms, but in a compound the molecules are made up of as many kinds of atoms as there are elements in the compound. Changes in the composition of substances (called chemical changes) are due to rearrangements of the atoms and the formation of new molecules. The atoms, therefore, are the units of chemical combination. In the formation of new compounds they unite, and in the breaking up of existing compounds they separate.

The uniting of oxygen is no exception to this general law. All of its combinations are brought about by the uniting of its atoms. In the burning of carbon, for example, the atoms of oxygen and the atoms of carbon unite, forming molecules of the compound known as carbon dioxide. The chemical formula of this compound, which is CO_2, shows the proportion in which the atoms unite-one atom of carbon uniting with two atoms of oxygen in each of the molecules. The affinity of oxygen for other elements, and the affinity of other elements for oxygen, and for each other, resides in their atoms.

*Oxidation.*-The uniting of oxygen with other elements is termed _oxidation_. This may take place slowly or rapidly, the two rates being designated as _slow_ oxidation and _rapid_ oxidation. Examples of slow oxidation are found in certain kinds of decay and in the rusting of iron.

Combustion is an example of rapid oxidation. Slow and rapid oxidation, while differing widely in their effects upon surrounding objects, are alike in that both produce heat and form compounds of oxygen. In slow oxidation, however, the heat may come off so gradually that it is not observed.

*Movement of Oxygen through the Body.*-Oxygen has been shown in the preceding chapters to pa.s.s from the lungs into the blood and later to leave the blood and, pa.s.sing through the lymph, to enter the cells. That oxygen does not become a permanent const.i.tuent of the cells is shown by the constancy of the body weight. Nearly two pounds of oxygen per day are known to enter the cells of the average-sized person. If this became a permanent part of the cells, the body would increase in weight from day to day. Since the body weight remains constant, or nearly so, we must conclude that oxygen leaves the body about as fast as it enters. Oxygen enters the body as a _free_ element. The form in which it leaves the body will be understood when we realize the purpose which it serves and the method by which it serves this purpose.

*Purpose of Oxygen in the Body.*-The question may be raised: Is it possible for oxygen to serve a purpose in the body without remaining in it? This, of course, depends upon what the purpose is. That it is possible for oxygen to serve a purpose and at the same time pa.s.s on through the place where it serves that purpose, is seen by studying the combustion in an ordinary stove (Fig. 54). Oxygen enters at the draft and for the most part pa.s.ses out at the flue, but in pa.s.sing through the stove it unites with, or oxidizes, the fuel, causing the combustion which produces the heat.

[Fig. 54]

Fig. 54-*Coal stove* ill.u.s.trating rapid oxidation.

Now it is found that certain chemical processes, mainly oxidations, are taking place in the body. These produce the heat for keeping it warm and also supply other forms of energy,(45) including motion. It is the purpose of oxygen to keep up these oxidations and, by so doing, to aid in supplying the body with energy. It serves this purpose in much the same way that it supports combustion, _i.e._, by uniting with, or oxidizing, materials derived from foods that are present in the cells.

*Does Oxygen serve Other Purposes?*-It has been suggested that oxygen may serve the purpose of oxidizing, or destroying, substances that are injurious and of acting, in this way, as a purifying agent in the body. In support of this view is the natural tendency of oxygen to unite with substances and the well-known fact that oxygen is an important natural agent in purifying water. It seems probable, therefore, that it may to a slight extent serve this purpose in the body. It is probable also that oxygen aids through its chemical activity in the formation of compounds which are to become a part of the cells. Both of these uses, however, are of minor importance when compared with _the main use of oxygen_, which _is that of an aid in supplying energy to the body_.

*Oxygen and the Maintenance of Life.*-In the supplying of energy to the body, one of the conditions necessary to the maintenance of life is provided. Because oxygen is necessary to this process, and because death quickly results when the supply of it is cut off, oxygen is frequently called the supporter of life. This idea is misleading, for oxygen has no more to do with the maintenance of life than have the food materials with which it unites. Life appears to be more dependent upon oxygen than upon food, simply because the supply of it in the body at any time is exceedingly small. Being continually surrounded by an atmosphere containing free oxygen, the body depends upon this as a constant source of supply, and does not store it up. Food, on the other hand, is taken in excess of the body's needs and stored in the various tissues, the supply being sufficient to last for several days. When the supply of either oxygen or food is exhausted in the body, life must cease.

*The Oxygen Movement a Necessity.*-Since _free_ oxygen is required for keeping up the chemical changes in the cells, and since it ceases to be free as soon as it goes into combination, its continuous movement through the body is a necessity. The oxygen compounds must be removed as fast as formed in order to make room for more free oxygen. This movement has already been studied in connection with the blood and the organs of respiration, but the consideration of certain details has been deferred till now. By what means and in what form is the oxygen pa.s.sed _to_ and _from_ the cells?