CHAPTER VIII 



BIOELECTRIC MEASUREMENTS 



Howard J. Curtis, VanderbUt University 



A . Introduction 233 



1 . Structure of Cells and Tissues 235 



2 . Equivalent Circuits 235 



B . Potential Measurements 237 



1 . Origin of Bioelectric Potentials 237 



2 . Electrodes 241 



3 . Salt Bridges 245 



4 . Insulation 246 



5 . Insulating Materials 247 



C. Equipment for Potential Measurements 248 



1 . Electronic Amplifiers 248 



2 . Electrometer Amplifiers 249 



3 . Direct Current Amplifiers 250 



4 . Capacitor-Coupled Amplifiers 2^4 



5 . Limitations of Amplifiers 255 



6 . Power Supplies 258 



7 . Recording Equipment 258 



D . Bioelectric Potentials 259 



1 . Membrane and Action Potentials in Nerve and Muscle. . . 259 



2 . Electrical Potentials around Tissues 262 



E . Impedance Measurements 262 



1 . Introduction 262 



2 . Equivalent Circuit 264 



3. Methods of Measurement 265 



4. Cell Constants as Measured by Impedance 267 



References 269 



A. INTRODUCTION 



The problem of the electrical characteristics of cells and tissues 

 has been of interest to biologists for a great many years. Indeed 

 it can almost be said that electricity was first discovered as a biologi- 

 cal phenomenon. For many years biological indicators were used to 

 detect the presence of electricity, and the strength of a voltaic pile 



233 



