196 



UNCONSCIOUS NERVOUS OPERATIONS 



piece of apparatus as shown in Fig. 106. The standard A B repre- 

 sents the vertebral column ; the two pieces CD and EF represent two 

 of the ribs, with Z)F, a portion of the sternum, attached ; a and b are 

 rubber bands representing the external and internal intercostal muscles 

 respectively ; c is a rubber band of such strength that it Keeps the 



Fig. 106. Apparatus to illustrate the movements of the ribs and 

 sternum in respiration. 



apparatus in position I when the rubber bands a and b are both on. 

 Remove the rubber band a ; Z>Fis lowered. Replace a and remove b ; DF 

 is raised. Observe that when DF is raised from position IT, the dis- 

 tance between DF and CE is increased, unless DF is raised too far. 



86. To show the Moisture in Respired A ir. Breathe upon a cool plate 

 of glass; some of the vapor in the breath will be condensed upon the 

 glass. To show that the presence of moisture is due to respiration, 

 blow upon the glass w r ith bellows. 



87. To show that A ir is made Warmer in Respiration. Notice the 

 reading of a thermometer, then breathe upon its bulb. 



88. Some Properties of the Constituent Gases of A ir. The teacher 

 should prepare oxygen, nitrogen, and carbon dioxide by methods 

 given in ordinary text-books of chemistry. Place a smoldering 

 splinter of wood in a vessel of oxygen ; the stick bursts into flame. 

 Place the flaming splinter in a vessel of carbon dioxide or nitrogen ; 

 the flame is at once extinguished. Place a blazing splinter in an 

 empty jar, i.e. containing only air; after burning some time it goes 

 out. Before the last trace of fire disappears, transfer the splinter to 

 a jar of oxygen; it burns actively again. Into a clean, empty jar put 

 a little limewater, prepared by dissolving lime in water. Cover the 

 jar and shake it well; if any considerable amount of carbon dioxide is 

 present, a white precipitate will form in the limewater. Now place 

 a burning splinter in the jar and allow it to burn out. Then shake 



