10 GENERAL PROPERTIES OF LIVING TISSUES 



ally to the nerve. The effect produced by 

 the nerve impulse depends on the nature of 

 the tissue in which the nerve ends ; for ex- 

 ample, the energy set free in secreting glands 

 is especially chemical; that set free in the 

 electrical organ of Torpedo is especially elec- 

 trical. In considering these illustrations of the 

 ways in which the energy of living tissue may 

 be set free, however, two facts should always 

 be kept in mind ; first, that by far the greater 

 part of the stored energy of the body is set 

 free as heat; and secondly, that while the sev- 

 eral tissues are characterized by the especial 

 prominence of some one form of energy, as 

 contractility in the case of muscle, and the 

 production and conveyance of a nerve impulse 

 in the case of nerve, yet the transformation of 

 energy in each tissue is a complex process, 

 many steps of which, for example heat and 

 chemical action, are common to all living 

 substance. 



We have made, then, the fundamental obser- 

 vation that an adequate stimulus will occasion 

 in muscle a conversion of latent energy into 

 mechanical change in form and in the nerve a 

 molecular change that passes along the nerve as 

 a nerve impulse. We must now examine sys- 

 tematically the usual methods of exciting the 



