THE VITAL PHENOMENA OF CELLS 



49 



We find similar skin currents in all Mammalia including man. If the 

 two hands or the two feet of a man be led off symmetrically to the gal- 

 vanometer and one arm or one foot be moved voluntarily the needle makes 

 an excursion, which is not caused by the muscular contraction in itself but 

 by the process of secretion going on at the same time in the sweat glands of 

 the contracted extremity. This current passes from the outside to the inside 

 of the skin. A very similar skin current has been observed in the sweating 

 of different mammals. 



Biedermann observes that one cannot draw a sharp line of separation between 

 current of rest and current of action in epithelial and glandular cells, for the 

 reason that the differences of tension met with 

 are always the expression of differences in the 

 chemical relations of the neighboring parts. From 

 this point of view it appears quite arbitrary, or 

 incorrect indeed, to speak of the current of rest 

 in contradistinction to the current of action of a 

 glandular structure, since in both cases one deals 

 with the effects of certain metabolic processes 

 going on in definite parts of the cell body, which 

 by direct or indirect stimulation are only changed 

 in one direction or another. It is better, there- 

 fore, to say that the ordinary skin current is pro- 

 duced by the negativity of that portion of the cell 

 which is being transformed into mucus, toward 

 the protoplasmic portion (Hermann). 



As above remarked, this inwardly directed 

 current may, under certain circumstances, un- 

 dergo a complete reversal. To explain this we 

 can make only one assumption, namely, that the 

 same epithelial cell has the power to act electri- 

 cally sometimes in one sense, sometimes in the 

 other. This is borne out by the fact that each 

 cell is the seat of two different chemical processes 

 (assimilation and dissimilation), which, going on 

 at the same time, give rise to opposite tensions. 

 The deviation occasionally observed would, ac- 

 cording to this, always be the resultant of the 

 two antagonistic forces (Hering, Biedermann). 



It is possible that a relationship similar to this exists between the chemical 

 processes underlying the secretion of water on the one hand and the secretion 

 of organically specific constituents on the other (Biedermann). Perhaps from 

 this point of view are to be explained certain results obtained with the digestive 

 glands, of which more in Chapter VII. 



Electrical currents have been demonstrated even in plants, where, just as 

 in the animal tissues, an injured place is found to be electro-negative to an 

 uninjured place. Electrical effects appear also under appropriate circum- 

 stances in certain parts of plants which are entirely uninjured. Thus, differ- 

 ences of tension are obtained between cells or cell territories of an organ or 

 of a whole plant which maintain different chemical relations to each other. 



For example, according to Waller, the processes taking place in the forma- 



FIG. 30. The cramp fish, Torpedo, 

 dissected to show electric ap- 

 paratus, after Huxley; 6, gills; 

 c, brain; e, electric organ; g, 

 cranium; me, spinal cord; np, 

 branches of pneumogastric 

 nerves to electric organs ; o, eye. 



