658 



PRINCIPLES OF GENERAL PHYSIOLOGY 



chloride, 0'6 per cent., is then applied, and subsequently a regular series of beats 

 with a large initial deflection made its appearance. This disappeared again when 

 the calcium salt was washed away with sodium chloride. 



The electro-positive change occurring in inhibition, observed by Gaskell and 

 others (p. 407), has been already discussed. 



Secreting Glands. The electrical changes in the salivary glands have been 

 described above (pages 350-352). Fig. 93 (page 351) represents them. Certain con- 

 clusions as to the secretory process were drawn from them. Electrical effects in 

 other glands were also mentioned, especially those of Hermann and Luchsingef 

 on the frog's tongue and on the sweat glands of the cat (1878, 1 and 2). 



The skin of the frog is also a structure containing simple glands, on which 

 considerable work has been done. That of L. and E. Orbeli (1910), which 

 contains full references to the earlier work, may be especially referred to here. 

 These observers show that the direction of the response to nerve stimulation varies 



with the solution used on the leading off 

 electrodes. With water alone the current 

 is an inflowing one, that is, the outer 

 surface becomes negative ; with sodium 

 chloride, 0-055 to 0'7 per cent., it becomes 

 positive. With potassium chloride the 

 effect is the same as with water, but pre- 

 ceded by a small deflection in the opposite 

 direction. The interpretation of the facts 

 is not easy, but the occurrence of an 

 electrical change in the presence of water 

 electrodes shows that it is not merely due 

 to the ions of the electrodes. Also, the 

 occurrence of two changes in two different 

 directions indicates the existence of two 

 processes in the gland cells, as discussed 

 above (page 352). 



If we suppose that we lead off from 

 opposite ends of a gland cell and that one 

 end becomes permeable when secretion 

 occurs, it is clear that we obtain then the 

 potential of the Helmholtz double layer, 

 since we obtain access, as it were, to the 

 interior of the cell. Thus, if the cell mem- 

 brane is, at rest, permeable to certain 

 anions only, we obtain an effect of the sign 

 of that associated with stimulation of the 

 chorda tympani nerve in the dog. This 

 view is in agreement with the theory of secretion given above (page .'5."> I ). 



Electrical Fish. The capability of certain fishes to give powerful electric 

 shocks, amounting to a potential difference of two or three hundred volts, might 

 appear puzzling until we remember that the electric organs are composed of a 

 large number of plates, arranged in series, and that these plates are excited 

 simultaneously by nerve fibres, so that a certain small potential difference is 

 established between the opposite sides of each plate. 



We see that there is no wave of excitation and, experimentally, the electrical change 

 is found to be a discharge, or series of rhythmic discharges, in one direction only. 



With the exception of that of Malapterurus, the electrical organs appear to be 

 formed of modified skeletal muscle. It has been suggested by Gotch that the 

 electrical change is that of the nerve end-plate. The muscular structure itself has 

 almost disappeared, but Fig. 216 shows that an apparently complex arrangement 

 of papillae has taken its place. It is interesting to note that, although the organ 

 of Malapterurus is developed from skin glands, its structure is very similar to that 

 of other fish, so that there must be some significance in those parts present in 

 addition to the nerve end-plaAes of the original muscle fibres. 



Fio. 214. SIMULTANEOUS RECORDS OF 



INTKAVENTRICULAR PRESSURE (riTKIl 



CURVE) AND ELECTRICAL CHANGE 

 (LOWER CURVE) OF THE CAT'S HEART. 



Klrrtrodes on auricle and ventricle. Time in 



truths of a second. 

 Note that the electrical change continues during 



the period of relaxation of the ventricle. 



(After Piper.) 



