1. A sheep's lungs with the windpipe attached may be readily obtained from a butcher. It is best to secure it and the heart all in one mass, as unless the heart be carefully removed holes are apt to be cut in the lung.

2. Examine the windpipe, and trace it down to its division into the bronchi. In the wall of the windpipe note the horse shoe shaped cartilages which keep it open, and which are so arranged that the dorsal aspect of the tube (which lies against the gullet) has no hard parts in it.

3. Trace one bronchus to its lung, and then cutting away the lung tissues follow the branching bronchial tubes through the organ. Note the cartilages in their walls.

4. Carefully divide the other bronchus where it joins the windpipe, and lay it and its lung aside. Then slit open the trachea, the bronchus still attached to it and the bronchial tubes. Observe the soft pale-red mucous membrane lining them.

5. In the bronchus which has still an uninjured lung attached to it tic air-tight a few inches of glass or other tubing of convenient size. On the end of the glass tube then slip a few inches of rubber tubing. On blowing through the rubber tube the lung will be distended, and as soon as the opening is left free it will collapse; in this way its great extensibility and elasticity will be seen.

6. Blow up the lung moderately, and while it is distended tie a string very tightly around the bit of rubber tubing. This will keep the air from escaping; the distended lung can now be examined at leisure, and its form, lobes, and the smooth moist pleura covering it be better seen than when it is collapsed.

7. To construct the very instructive mode! depicted in Fig. 67, obtain a wide necked glass vessel, and a rubber toy balloon. Very carefully untie and open the neck of the balloon, and tie into it tightly a glass rod. Take a cork (one of rubber is best) which fits the neck of the bottle tightly and is perforated by two holes; through one of these holes pass the tube projecting from the neck of the balloon in such way that the collapsed balloon is on the under side of the cork. Through the other hole pass, air tight, a tube bent as shown in the figure and on the upper end of this slip a few inches of rubber tubing. (This can be pinched or tied up at any time, and in that way closed, and so forms a cheap substitute for the stopcock represented in the figure). When the cork is now secured firmly in the bottle the apparatus is ready for use as indicated on p. 269.

8. Substitute a lung for the rubber balloon in the above experiment.

9. The action of the diaphragm may be illustrated by substituting for the bottle of § 7 a bell-jar with a wide neck at its upper end. Take a piece of sheet rubber somewhat larger than the bottom of the bell-jar, and tie a button or marble in the centre of it Lay the rubber on the table, with the projection caused by the button downwards. On it place the bell jar, stretch the rubber moderately tight, turn its edges up around the margin of the bell jar, and tie very tightly with waxed cord or copper wire. In the neck of the bell-jar place a tight cork with tubes and rubber balloon, as described in § 7. Suck air out of the bottle until the balloon is fairly well expanded ; then tie the rubber tube., As the air is removed the pressure of the atmosphere on its exterior will cause the rubber sheet to arch up into the cavity of the bell-jar so that it now fairly well represents the diaphragm. The knob caused by the button serves as a handle by which this artificial diaphragm may be pulled down, representing inspiration; as it descends the balloon (lung) enlarges, and air enters it from outside. When the button is let go the artificial diaphragm ascends, the lung collapses, and air is forced out of it (expiration). Then open the air tube leading into the bell-jar. The lung will collapse, and the movements of the diaphragm have no influence upon it.

10. The diaphragm itself may be readily seen on the body of any small animal (rat, kitten, puppy), on removing the abdominal viscera. The liver and stomach must be cut away with especial care.

a. When the above viscera are removed the vaulted diaphragm will be seen, and through it the pink lungs.

b. Seizing some of the folds of peritoneum attached to the diaphragm, pull it down, imitating its contraction and flattening in inspiration. The lungs will be seen to follow it closely, expanding to fill the space left by it in its descent.

e. Make a free opening into one side of the thorax. The corresponding lung will collapse, and be no longer influenced by movements of the diaphragm.

d. Now open the other side of the chest: its lung also shrinks up; the structure of the diaphragm (its tendinous centre a»d muscular peripheral regions) can now be better seen, as also the attachment of the pericardium to its thoracic side.

11. The action of the microscopic cilia in driving along the mucus in which they move may be demonstrated as follows: a. Cut off a frog's head and destroy its spinal cord (p. 258). Then cut out its gullet as completely as possible; slit this open and spread it out, inner side up, on a piece of cork or board, and fix it with pins stuck through its edges.

b. Prepare a very thin and small shaving of cork. Dissect the skin off one thigh of the animal and wrap a bit of it round the shaving of cork, with its under side outwards.

c. Place the light mass thus formed on the mucous membrane of the gullet, near its mouth end. The little mass will slowly be moved along to the stomach end of the gullet, and if returned to the mouth end time after time will be swept along in the same direction. This is due to the cilia which line the frog's gullet (they are not present in that of man), and push along to the stomach the mucus bathing them on which the little float swims.

d. Place the exposed gullet under a bell-jar with a wet sponge for an hour or two. The mucus secreted by it will be found to have been swept along to the end of it which joins the stomach.