ANIMAL AND VEGETABLE 251 



CHAPTER XIX 



THE INTERPRETATION OF CERTAIN 

 ELECTRO-PHYSIOLOGICAL PHENOMENA 



THERE are in the human body many structures and 

 substances which, although not in themselves of very high 

 resistance, may, in view of the low tension of the nerve- 

 current, be termed dielectrics. Among these are the 

 sheaths of medullated and the lipoid coatings of non- 

 medullated nerves ; the capsules and membranous cover- 

 ings of and in cells ; the sarcolemma and neurilemma ; 

 Krause's membranes of voluntary muscular tissue, neu- 

 roglia processes and connective tissue, etc. 



The effect of heat upon any and every known dielectric 

 is to lower its resistance. 



To ascertain, for instance, the relative resistance of 

 gutta-percha at different temperatures we have the 

 formula 



Log R = log r t log 0-9399 



where R = resistance at higher temperature, 



r resistance at lower temperature, and 

 / = difference in temperature in degrees F. 



Reduced to figures, the relative resistances, calculated 

 from the curve, are : 75 F. = 1-000 ; 90 F. = 0-407; 

 100 F. = 0-223 ; 110 F. = 0-137. 



In acute inflammation the local temperature that is, 

 the temperature in the area affected may rise at least ten 

 degrees F. above normal ; and this would, for gutta- 

 percha, give us 0-4068 (at 90 F.) and 0-2238 (at 100 F.), 



