20 INTRODUCTION. LiECT. I. 



the trachea, you perceive that the lung collapses ; whilst 

 it swells up and expands again when I force air into it. 

 Do not imagine that these different organs could fulfil 

 their respective functions without the elasticity of the pa- 

 renchyma of the lung, of the intestine, or of the artery. 

 Destroy this, and these functions are stopped, or at the 

 least they are altered. 



Gravity. Gravity acts upon the solid, liquid, and 

 gaseous parts of living beings, as on all other natural 

 bodies. We could never explain the functions of respira- 

 tion and absorption if we did not take into consideration 

 the physical properties of the solids, liquids, and gases of 

 the economy, and their conditions of equilibrium. 



Caloric. Apply a sufficient degree of heat to an orga- 

 nic body, and you will observe the evolution of gas, the 

 disengagement of aqueous vapour, and the combustion of 

 carbon and hydrogen in the air, producing carbonic acid 

 and water. If at first the heat frequently hardens and 

 shrivels organic matters, instead of dilating and liquefy- 

 ing them, as it usually does with inorganic substances, you 

 cannot surely attribute this difference to vital action, since 

 life has long been extinct when these phenomena appear. 



All these effects are owing to a peculiar structure and to 

 the physico-chemical properties of the elements of which 

 the tissues are composed. In fact, organized beings, when 

 subjected to the action of heat, first lose the water with 

 which they are impregnated, an effect which commences 

 in the part to which the heat is most directly applied ; the 

 substance then curls up like horn, just as a piece of paper 

 does which has been moistened more on one side than on 

 the other, the largest surface forming the convexity of the 

 new shape produced by the contraction. 



These organic bodies often contain albumen, which coa- 



