734 A MANUAL OF PHYSIOLOGY 



cortex cerebri, they obtained a persistent negative 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 

 investigations on the paths by which impulses set up at different 

 points travel along the cord. To these we shall have to refer 

 again (p. 793). 



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 submaxillary 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. 288). When the 

 chorda tympani is stimulated with 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 

 FIG. 288. CURRENT OF SUB- containing glands the current is chiefly, 

 MAXILLARY GLAND. but not altogether, secretory. 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 stimula- 

 tion 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 mem- 

 brane, which has the same direction as that of the skin cf 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 influences 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 been 

 observed in the frog's tongue on excitation of the glosso-pharyngeal 

 nerve. 



Eye-currents. If two unpolarizable electrodes connected with 

 a galvanometer are placed on the excised eye of a frog or rabbit, 

 one on the cornea and the other on the cut optic nerve, or on the 

 posterior surface of the eyeball, it is found that a current passes in 

 the eye from optic nerve to cornea, the fundus of the eye being 



