THE REASON WHY t 



1 Man flies from tirae, and time from man ; too soon 

 In sad divorce this double flight must end." YOUNG. 



three lobes of the right lung and the two lobes of the left lung are shown in their 

 proper positions, g is the windpipe through which air is admitted. 



84. Why are the lungs capable of indicating whether an infant 

 found dead has been still-born or not ? 



Because lungs which have never breathed are heavier than 

 water, and sink ; but lungs which have breathed, if only once, are 

 lighter than water, and swim. 



85. The lungs, previously to birth, are compressed like a squeezed sponge, and ex- 

 pand whenever the pressure is taken off. The moment they expand tbe air rushes 

 in by the nostrils and mouth ; and the force with which it enters causes the expan- 

 sion a little beyond the natural state. This acts as a stimulus upon the muscles, 

 which immediately contract, diminish the cavity of the chest, and, in conjunction 

 with the elasticity of the lungs, expel the air till the lungs are again reduced to less 

 than their natural capacity, and this stimulates the antagonists of the former 

 muscles, namely, those which expand the chest, and they assist the pressure of the 

 atmosphere in again filling the lungs. The expansion of the lungs is always pro- 

 duced by their own elasticity, for no muscular apparatus could work so fine a 

 structure ; but the expansion of the chest gives room ; and the contraction of the 

 chest again occasions the expulsion. Thus the lungs are set going by atmospheric 

 pressure and elasticity ; and the action is kept up and regulated by this and 

 muscular force conjointly. 



8& Why does the chest 

 heave when we breathe ? 



Because when we inspire 

 the air, the ribs are drawn 

 upward and outward, and the 

 diaphragm at the same time 

 is fouied down. When we 

 expire the air, the ribs return 

 to their natural place, whilst 

 the diaphragm is again 

 drawn up. 



87. In the accompanying illustra- 

 tion, the front half of the ribs being 

 cut away, the interior cf the chest is 

 exposed. C C is the cavity of the 

 chest, empty. D D 1) D the dia- 

 phragm, rising high in the centr" 



