A Practical Physiology Part 45

Experiment 193. _To examine white fibrous tissue._ Snip off a very minute portion from the muscle of a rabbit, or any small animal recently dead. Tease the specimen with needles, mount in salt solution and examine under a high power. Note the course and characters of the fibers.

Experiment 194. _To examine elastic tissue._ Tease out a small piece of ligament from a rabbit's leg in salt solution; mount in the same, and examine as before. Note the curled elastic fibers.

Experiment 195. _To examine areolar tissue._ Gently tease apart some muscular fibers, noting that they are attached to each other by connective tissue. Remove a little of this tissue to a slide and examine as before. Examine the matrix with curled elastic fiber mixed with straight white fibers.

Experiment 196. _To examine adipose tissue._ Take a bit of fat from the mesentery of a rabbit. Tease the specimen in salt solution and mount in the same. Note the fat cells lying in a vascular meshwork.

Experiment 197. _To examine connective tissues._ Take a very small portion from one of the tendons of a rabbit, or any animal recently dead; place upon a gla.s.s slide with a drop of salt solution; tease it apart with needles, cover with thin gla.s.s and examine with microscope.

The fine wavy filaments will be seen. Allow a drop of dilute acetic acid to run under the cover gla.s.s; the filaments will swell and become transparent.

Experiment 198. Tease out a small piece of ligament from the rabbit's leg in salt solution; mount in the same, and examine under a high power. Note the curled elastic fibers.

Experiment 199. _A crude experiment to represent the way in which a person's neck is broken._ Bring the ends of the left thumb and the left second finger together in the form of a ring. Place a piece of a wooden toothpick across it from the middle of the finger to the middle of the thumb. Put the right forefinger of the other hand up through the front part to represent the odontoid process of the axis, and place some absorbent cotton through the other part to represent the spinal cord.

Push backwards with the forefinger with just enough force to break the toothpick and drive its fragments on to the cotton.

Experiment 200. _To ill.u.s.trate how the pulse-wave is transmitted along an artery._ Use the same apparatus as in Experiment 106, p. 201.

Take several thin, narrow strips of pine wood. Make little flags by fastening a small piece of tissue paper on one end of a wooden toothpick. Wedge the other end of the toothpick into one end of the strips of pine wood. Use these strips like levers by placing them across the long rubber tube at different points. Let each lever compress the tube a little by weighting one end of it with a blackboard eraser or book of convenient size.

As the pulse-wave pa.s.ses along under the levers they will be successively raised, causing a slight movement of the tissue-paper flags.

Experiment 201. _The dissection of a sheep's heart._ Get a sheep's heart with the lungs attached, as the position of the heart will be better understood. Let the lungs be laid upon a dish so that the heart is uppermost, with its apex turned toward the observer.

The line of fat which extends from the upper and left side of the heart downwards and across towards the right side, indicates the division between the right and left ventricles.

Examine the large vessels, and, by reference to the text and ill.u.s.trations, make quite certain which are the _aorta_, the _pulmonary artery_, the _superior_ and _inferior venae cavae_, and the _pulmonary veins_.

Tie variously colored yarns to the vessels, so that they may be distinguished when separated from the surrounding parts.

Having separated the heart from the lungs, cut out a portion of the wall of the _right ventricle_ towards its lower part, so as to lay the cavity open. Gradually enlarge the opening until the _chordae tendineae_ and the flaps of the _tricuspid valve_ are seen. Continue to lay open the ventricle towards the pulmonary artery until the _semilunar valves_ come into view.

The pulmonary artery may now be opened from above so as to display the upper surfaces of the semilunar valves. Remove part of the wall of the right auricle, and examine the right auriculo-ventricular opening.

The heart may now be turned over, and the _left ventricle_ laid open in a similar manner. Notice that the mitral valve has only two flaps. The form of the valves is better seen if they are placed under water, and allowed to float out. Observe that the walls of the _left_ ventricle are much thicker than those of the _right_.

Open the left auricle, and notice the entrance of the _pulmonary veins_, and the pa.s.sage into the ventricle.

The ventricular cavity should now be opened up as far as the aorta, and the semilunar valves examined. Cut open the aorta, and notice the form of the _semilunar valves_.

Experiment 202. _To show the circulation in a frog's foot_ (see Fig. 78, p. 192). In order to see the blood circulating in the membrane of a frog's foot it is necessary to firmly hold the frog. For this purpose obtain a piece of soft wood, about six inches long and three wide, and half an inch thick. At about two inches from one end of this, cut a hole three-quarters of an inch in diameter and cover it with a piece of gla.s.s, which should be let into the wood, so as to be level with the surface. Then tie up the frog in a wet cloth, leaving one of the hind legs outside. Next, fasten a piece of cotton to each of the two longest toes, but not too tightly, or the circulation will be stopped and you may hurt the frog.

Tie the frog upon the board in such a way that the foot will just come over the gla.s.s in the aperture. Pull carefully the pieces of cotton tied to the toes, so as to spread out the membrane between them over the gla.s.s. Fasten the threads by drawing them into notches cut in the sides of the board. The board should now be fixed by elastic bands, or by any other convenient means, upon the stage of the microscope, so as to bring the membrane of the foot under the object gla.s.s.

The flow of blood thus shown is indeed a wonderful sight, and never to be forgotten. The membrane should be occasionally moistened with water.

Care should be taken not to occasion any pain to the frog.

Experiment 203. _To ill.u.s.trate the mechanics of respiration_[58]

(see Experiment 122, p. 234). "In a large lamp-chimney, the top of which is closed by a tightly fitting perforated cork (A), is arranged a pair of rubber bags (C) which are attached to a Y connecting tube (B), to be had of any dealer in chemical apparatus or which can be made by a teacher having a bunsen burner and a little practice in the manipulation of gla.s.s (Fig. 171). From the center of the cork is attached a rubber band by means of a staple driven through the cork, the other end of which (D) is attached to the center of a disk of rubber (E) such as dentists use. This disk is held to the edge of the chimney by a wide elastic band (F). There is a string (G) also attached to the center of the rubber disk by means of which the diaphragm may be lowered.

[Ill.u.s.tration: Fig. 171.]

Such is a description of the essentials of the model. The difficulties encountered in its construction are few and easily overcome. In the first place, the cork must be air-tight, and it is best made so by pouring a little melted paraffin over it, care being taken not to close the tube. The rubber bags were taken from toy balloon-whistles.

In the construction of the diaphragm, it is to be remembered that it also must be air-tight, and in order to resemble the human diaphragm, it must have a conical appearance when at rest. In order to avoid making any holes in the rubber, the two attachments (one of the rubber band, and the other of the string) were made in this wise: the rubber was stretched over a b.u.t.ton having an eye, then under the b.u.t.ton was placed a smaller ring from an old umbrella; to this ring was attached the rubber band, and to the eye of the b.u.t.ton was fastened the operating string. When not in use the diaphragm should be taken off to relieve the strain on the rubber band."

Experiment 204. _To ill.u.s.trate the action of the intercostal muscles_ (see sec. 210). The action of the intercostal muscles is not at first easy to understand; but it will be readily comprehended by reference to a model such as that represented in Fig. 172. This maybe easily made by the student himself with four laths of wood, fastened together at the corners, A, B, C, D, with pins or small screws, so as to be movable. At the points E, F, G, H, pins are placed, to which elastic bands may be attached (A). B D represents the vertebral column; A C, the sternum; and A B and C D, the ribs. The elastic band F G represents the _external_ intercostal muscles, and E H, the _internal_ intercostals.

[Ill.u.s.tration: Fig. 172.]

If now the elastic band E H be removed, the remaining band, F G, will tend to bring the two points to which it is attached, nearer together, and the result will be that the bars A B and C D will be drawn upwards (B), that is, in the same direction as the ribs in the act of _inspiration_. When the elastic band E H is allowed to exert its force, the opposite effect will be produced (C); in this case representing the position of the ribs in an act of _expiration_.

Experiment 205. Pin a round piece of bright red paper (large as a dinner-plate) to a white wall, with a single pin. Fasten a long piece of thread to it, so it can be pulled down in a moment. Gaze steadily at the red paper. Have it removed while looking at it intently, and a greenish spot takes its place.

Experiment 206. Lay on different parts of the skin a small, square piece of paper with a small central hole in it. Let the person close his eyes, while another person gently touches the uncovered piece of skin with cotton wool, or brings near it a hot body. In each case ask the observed person to distinguish between them. He will always succeed on the volar side of the hand, but occasionally fail on the dorsal surface of the hand, the extensor surface of the arm, and very frequently on the skin of the back.

Experiment 207. _Wheatstone's fluttering hearts_. Make a drawing of a red heart on a bright blue ground. In a dark room lighted by a candle hold the picture below the level of the eyes and give it a gentle to-and-fro motion. On continuing to look at the heart it will appear to move or flutter over the blue background.

Experiment 208. At a distance of six inches from the eyes hold a veil or thin gauze in front of some printed matter placed at a distance of about two feet. Close one eye, and with the other we soon see either the letters distinctly or the fine threads of the veil, but we cannot see both equally distinct at the same time. The eye, therefore, can form a distinct image of a near or distant object, but not of both at the same time; hence the necessity for accommodation.

Experiment 209. Place a person in front of a bright light opposite a window, and let him look at the light; or place one's self opposite a well-illuminated mirror. Close one eye with the hand and observe the diameter of the other pupil. Then suddenly remove the hand from the closed eye: light falls upon it; at the same time the pupil of the other eye contracts.

Experiment 210. _To ill.u.s.trate the blind spot. Marriott's experiment_. On a white card make a cross and a large dot, either black or colored. Hold the card vertically about ten inches from the right eye, the left being closed. Look steadily at the cross with the right eye, when both the cross and the circle will be seen. Gradually approach the card toward the eye, keeping the axis of vision fixed on the cross.

At a certain distance the circle will disappear, i.e., when its image falls on the entrance of the optic nerve. On bringing the card nearer, the circle reappears, the cross, of course, being visible all the time (see Experiment 180, p. 355).

Experiment 211. _To map out the field of vision_. A crude method is to place the person with his back to a window, ask him to close one eye, stand in front of him about two feet distant, hold up the forefingers of both hands in front of and in the plane of your own face. Ask the person to look steadily at your nose, and as he does so observe to what extent the fingers can be separated horizontally, vertically, and in oblique directions before they disappear from his field of vision.

Experiment 212. _To ill.u.s.trate imperfect judgment of distance_.

Close one eye and hold the left forefinger vertically in front of the other eye, at arm's length, and try to strike it with the right forefinger.

On the first trial one will probably fall short of the mark, and fail to touch it. Close one eye, and rapidly try to dip a pen into an inkstand, or put a finger into the mouth of a bottle placed at a convenient distance. In both cases one will not succeed at first.

In these cases one loses the impressions produced by the convergence of the optic axes, which are important factors in judging of distance.

Experiment 213. Hold a pencil vertically about twelve inches from the nose, fix it with both eyes, close the left eye, and then hold the right index finger vertically, so as to cover the lower part of the pencil. With a sudden move, try to strike the pencil with the finger. In every case one misses the pencil and sweeps to the right of it.

Experiment 214. _To ill.u.s.trate imperfect judgment of direction_. As the retina is spherical, a line beyond a certain length when looked at always shows an appreciable curvature.

Hold a straight edge just below the level of the eyes. Its upper margin shows a slight concavity.

Surface Anatomy and Landmarks.

In all of our leading medical colleges the students are carefully and thoroughly drilled on a study of certain persons selected as models. The object is to master by observation and manipulation the details of what is known as surface anatomy and landmarks. Now while detailed work of this kind is not necessary in secondary schools, yet a limited amount of study along these lines is deeply interesting and profitable. The habit of looking at the living body with anatomical eyes and with eyes at our fingers' ends, during the course in physiology, cannot be too highly estimated.

In elementary work it is only fair to state that many points of surface anatomy and many of the landmarks cannot always be defined or located with precision. A great deal in this direction can, however, be done in higher schools with ingenuity, patience, and a due regard for the feelings of all concerned. Students should be taught to examine their own bodies for this purpose. Two friends may thus work together, each serving as a "model" to the other.

To the following syllabus may be added such other similar exercises as ingenuity may suggest or time permit.