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 glass slide with a drop of salt solution; tease it apart with needles, cover with thin glass and examine with microscope. The fine wavy filaments will be seen. Allow a drop of dilute acetic acid to run under the cover glass; 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 illustrate 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 passes 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 illustrations, make quite certain which are the aorta, the pulmonary artery, the superior and inferior venæ cavæ, 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 chordæ tendineæ 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 passage 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 glass, 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 glass in the aperture. Pull carefully the pieces of cotton tied to the toes, so as to spread out the membrane between them over the glass. 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 glass.
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 illustrate 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 glass ([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.
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 button having an eye, then under the button was placed a smaller ring from an old umbrella; to this ring was attached the rubber band, and to the eye of the button was fastened the operating string. When not in use the diaphragm should be taken off to relieve the strain on the rubber band.”
