RESPIRATION AND EXCRETION 



293 



loons when the rubber (diaphragm) is pulled down ? When 

 relaxed ? 



2. What is the position of the rubber in each case ? 



Conclusions. 1. Is 

 there more or less 

 room in the bell jar 

 (chest) when the rub- 

 ber (diaphragm) is 

 pulled down ? 



2. Compare the ef- 

 fect of the rubber with 

 the function of the 

 diaphragm in your 

 body. (See chart or 

 Figures for the loca- 

 tion of the diaphragm.) 



3. THE RIBS 



Materials. Make a 

 model like Figure 72 FlG> 72> ~ Dia s ram showing action of the ribs, 

 a, position during expiration ; 6, position during 

 using a strip of wood ins pi ration . 



to represent the back- 

 bone, and other strips to represent the ribs and breastbone. 

 Use small nails to form loose joints at the corners. Use a cord 

 for the diagonal. 



Method. Hold the apparatus as in Figure 72 and pull the 

 cord ed in the direction of the arrow. Note what happens. 



Observations. 1. What change in the distance between ec 

 (breastbone) and df (backbone) when de is pulled ? Note. 

 If cd and ef represent ribs, what does ed represent? 



2. The ribs by their own elasticity bring the breastbone from 

 the position b to the position a. Are the ribs fastened to the 

 backbone with joints as in the apparatus ? 



Conclusions. 1. What effect on the capacity of the chest 

 when the muscles pull the ribs upwards and outwards ? 



