8 1 o ELECTRO-PH YSIOLOG Y 



hands, or, better, with the right hand and the left foot. The two feet 

 are the most unfavourable combination. The reason is obvious from 

 the direction of the long axis of the heart, which determines the 

 direction of the lines of flow of currents due to differences of potential 

 between base and apex (Fig. 301). 



Central Nervous System. It was discovered by du Bois-Reymonci 

 that the spinal cord, like a nerve, shows a current of rest between longi- 

 tudinal surface and cross-section, and that a current of action is caused 

 by excitation. Setschenow stated that when the medulla oblongata 

 of the frog was connected with a galvanometer, spontaneous variations 

 occurred which he supposed due to periodic functional changes in its 

 grey matter. Gotch and Horsley have made experiments on the spinal 

 cords of cats and monkeys. Leading off from an isolated portion of 

 the dorsal cord to the capillary electrometer, and stimulating the 

 ' motor ' region of the cortex cerebri, they obtained a persistent nega- 

 tive variation followed by a series of intermittent variations. This 

 agrees remarkably with the muscular contractions in an epileptiform 

 convulsion started by a similar excitation of the cortex, which consist 

 of a tonic spasm followed by clonic or phasic (interrupted) contractions. 

 By means of the galvanometer, the same observers have made in- 

 vestigations on the paths by which impulses set up at different points 

 travel along the cord. To these we shall have to refer again (p. 867). 

 Electrical Phenomena of Glands. These have been studied with any 

 care chiefly in the submaxillary gland and in the skin, although the 

 liver, kidney, spleen, and other organs also 

 show currents when injured. In the sub- 

 maxillary gland the hilus is galvanometrically 

 positive to any point on the external surface 

 of the gland; a current passes from hilus to 

 surface through the galvanometer, and from 

 surface to hilus through the gland (Fig. 306). 

 Fig. 306. Current of Sub- When the chorda tympani is stimulated with 

 maxillary Gland. rapidly - succeeding shocks of moderate 



strength, there is a positive variation i.e., the 



hilus becomes still more positive to the surface. This variation can 

 be abolished by a small dose of atropine. 



Skin Currents. So far as has been investigated, the integument of all 

 animals shows a permanent current passing in the skin from the external 

 surface inwards. This is feebler in skin which possesses no glands. In 

 skin containing glands the current is chiefly, but not altogether, secre- 

 tory. As such, it is affected by influences which affect secretion, a 

 positive variation being caused by excitation of secretory nerves e.g., 

 in the pad of the cat's foot by stimulation of the sciatic. The deflection 

 obtained when a finger of each hand is led off to the galvanometer, 

 which was at one time looked upon as a proof of the existence of currents 

 of rest in intact muscles, is due to a secretion current. 



Of more doubtful origin is the current of ciliated mucous membrane, 

 which has the same direction as that of the skin of the frog and the 

 mucous membrane of the stomach of the frog and rabbit viz., from 

 ciliated to under surface through the tissue, or from ciliated surface to 

 cross-section, if that is the way in which it is led off. The current is 

 strengthened by induction shocks, by heating, and in general by influ- 

 ences which increase the activity of the cilia. Some circumstances 

 point to the goblet-cells in the membrane as the source of the current; 

 but, on the whole, the balance of evidence is in favour of the cilia being 

 the chief factor (Engelmann), although the mucin-secreting cells may 

 be concerned, too. Electrical changes associated with secretion have 



