WHAT IS A LIVING ANIMAL? 293 



The insulatory resistance of the bare human skin varies from 1,000 to 

 6,000 ohms. In many animals the insulation is increased by non-con- 

 ducting hair, wool, fur, etc. And naked man finds it expedient to rein- 

 force his own insulation by clothing of silk, satin, hair, wool, flannel 

 and other non-conducting materials. We are exhilarated by a dry 

 atmosphere: depressed by a damp one, because the moist air, being a 

 conductor, carries off some of our electricity to the earth, while dry air 

 is a more complete insulator and prevents this leakage. 



Besides contact with the air, the feet of animals are in actual con- 

 tact with the earth itself, and accordingly ought to be endowed with a 

 specially good insulation. 



Finding no data on this point, I submitted to the TJ. S. Bureau of 

 Standards some specimens of a horse's hoof, to have their insulation 

 tested. The director, Professor S. W. Stratton, wrote me 5 that the 

 resistance of the first specimen, when dry, was 4,700 million ohms. 

 This was a part of the " frog " of the foot. A second specimen, taken 

 from the peripheral margin of the hoof was tested, of which the bureau 

 reported 6 that " by the direct-deflection method, using 120 volts and a 

 very sensitive galvanometer, the deflection was so small that it could 

 not be read." " The resistance was equal to or greater than 22 billion 

 ohms. This corresponds to a specific resistance of about 16.5 X 10 10 

 ohms per centimeter cube." Professor Stratton adds : " Of course the 

 actual resistance may be much higher, as it was too high to determine 

 with any accuracy by this means." 



Subsequently, Professor Chas. W. Mortimer, of the George Wash- 

 ington University, by using his Wheatstone Bridge apparatus, kindly 

 tested for me, altogether, 67 specimens of animal and some vegetable 

 structures, as to the insulating power of their external coverings. The 

 specimens included the feet, claws and bills of sheep, rabbits and chick- 

 ens; the fresh human umbilical cord, fcetal membranes and placenta; 

 the shell of an egg; the external coverings of fruits (oranges, apples, 

 nuts, etc.) and of vegetables (turnips, onions, etc.). 



In no instance did the external covering fail to exhibit a relatively 

 greater resistance than the internal structure. In most of the speci- 

 mens the resistance hovered about 10,000,000 ohms, some more, some 

 less. In one instance, that of a green pea pod, the resistance of the un- 

 broken pod was 500,000 ohms, while the external surface of the green 

 pea itself was 10,000,000 ohms. 



I did not test any cereal grains, but Mr. Lyman J. Briggs, of the 

 Bureau of Plant Industry, U. S. Department of Agriculture, has re- 

 cently ascertained that the resistance of wheat grains, varying with 



5 Official letter, October 23, 1903. 

 "Official letter, January 21, 1904. 



