248 THE HUMAN BODY. 



5. In the bronchus which has still an uninjured lung attached to 

 it tie 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 model 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 tbis slip a few inches 

 of rubber tubing. (Tins 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. 239. 



8. Substitute a lung for the rubber balloon in the above experi- 

 ment. 



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 rub- 

 ber on the table, with the projection caused by the button down- 

 wards. 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 ex- 

 panded; 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 



