892 SPECIAL PHYSIOLOGY. 



EVOLUTION OF ELECTRICITY. 



The electric currents constantly present in the living nervous and 

 muscular tissues, and the common electric current present in the entire 

 human body, and in the bodies of the lower animals generally, especi- 

 ally noticeable in the frog, have been elsewhere mentioned (pp. 138, 

 224). This common current usually passes from the lower extremities 

 to the head of an animal ; but in the upper limbs of the human body 

 it is said to be directed from the shoulder lo the fingers. Electric cur- 

 rents have also been detected upon different secreting surfaces and 

 glands, and even between a secreting membrane and the veins return- 

 ing from it. These phenomena cease with the life of the animal ex- 

 perimented upon. The direction of these currents is shown by delicate 

 galvanometers. Thus, currents pass from the venous blood, which is 

 positive, to the gland or secreting surface, which is negative ; no cur- 

 rent passes between a gland and the arterial blood. Arterial blood is 

 said to be positive as compared with venous blood. (Scoutetten.) Be- 

 tween the corresponding points of the two sides of the body, or of op- 

 posite limbs, no electric currents are ordinarily found ; but they occur 

 between non-correspondent points, and even between corresponding 

 points, if there is a difference with respect to their nutritive activity, 

 as when one limb is at rest and the other in motion, or as when one 

 limb is more or less inflamed. (Matteucci, Du Bois-Reymond.) The 

 electricity of the human body under ordinary circumstances is rapidly 

 conducted from it, and thus an equilibrium is maintained with respect 

 to surrounding media. But when the body is insulated its proper 

 electric state is speedily manifested, either when it is brought into con- 

 tact with non-insulated bodies, the galvanometer intervening, or when 

 two insulated persons are connected with the galvanometer or touch 

 each other. Thus examined, the electric condition of men is usually 

 positive, that of women is said more frequently to be negative. San- 

 guine and irritable persons exhibit a more active electric condition 

 than others. It is well known that electricity is sometimes developed 

 in the body by friction, or by the rapid removal of stockings, especi- 

 ally silk ones, or of other articles of dress which fit closely to the skin. 

 This phenomenon is accompanied by slight crackling noises, and even 

 by sparks, especially in dry weather, dry air being a better non-con- 

 ductor than moist, and so preventing the escape of the electricity of 

 the body. Remarkable and exceptional instances of the accumulation 

 of electricity in the human body are on record, in which, if the person 

 were only moderately insulated, sparks could readily be drawn from 

 any part of the body. 



The total quantity of electricity developed in the body must be very 

 large; but owing to the quantity of water in the tissues, to the high 

 conducting power of that fluid, and to the absence of arrangements 

 calculated to insulate the electric currents, the electricity passes as 

 soon as it is generated into a state of equilibrium. Moreover, this 

 animal electricity speedily acquires a condition of equilibrium, as re- 

 gards neighboring objects and media; and it is'only when the body is 



