12 GENERAL PROPERTIES OF LIVING TISSUES 



II 



METHODS OF ELECTRICAL STIMULATION 

 INTRODUCTION 



THE stimulus most usually employed in the 

 laboratory is electricity, because electricity will 

 stimulate when used in quantities which do not 

 destroy the tissues, as do many mechanical, 

 chemical, and thermal stimuli, and because the 

 intensity and duration of the electrical stimulus 

 can be graduated with accuracy. It will be 

 necessary, therefore, to examine with especial 

 care the methods and the results of electrical 

 stimulation. These matters are involved with 

 problems of ionisation, surface tension, osmosis, 

 and other molecular actions highly important 

 in many fields of physiology. Such interde- 

 pendent phenomena cannot be studied profitably 

 without working hypotheses that shall attempt 

 to relate them as forms of energy. 



Kinetic Theory. The particles of a gas, the 

 simplest state in which matter exists, are identi- 

 cal with its chemical molecules. These particles 



