GRAPHIC REGISTRATION OF MUSCULAR CONTRACTION 59 



one of them, provided the values of the other two are known. Thus: 



volts = amperes X ohms 

 amperes = volts 4- ohms 

 ohms = volts -T- amperes 



Polarization. The two metals of a battery, copper and zinc, 

 are surrounded by electrolytes, the tendency of which is to pass 

 toward the opposite pole. Thus, the positive ions, Cu and H, progress 

 toward the cathode, while the negative OH and SO 4 pass toward the 

 anode which, inside the cell, is the zinc. The copper plate then be- 

 comes covered with bubbles of hydrogen which finally place so high a 

 resistance in the path of the current that 

 it is neutralized and ceases to flow. This 

 action which is called polarization, finally 

 leads to the production of secondary 

 currents, the direction of which is oppo- 

 site to that of the primary one. It may 

 also happen that some of the sulphate 

 of zinc is attacked by the hydrogen and 

 is deposited upon the copper plate in the 

 form of a film of constantly increasing 

 thickness. This action must necessarily 

 lead to a reduction of the electromotive 

 force and finally to a cessation of the pri- 

 mary current. In the Daniell cell, the 

 occurrence of polarization is prevented 

 by the copper sulphate and in the 

 Le"clanche cell by the dioxid of man- 



ganese. 



FIG. 



29 . NON-POLARIZABLE 



ELECTRODES. 



M , muscle or nerve; C, cotton 

 or camel's hair brush; 8, solution 

 of zinc sulphate; Z, amalgamated 

 zinc. 



Under ordinary conditions the electrical cur- 

 rent is passed through living substance by means 

 of two copper wires which may be equipped 

 with small platelets of platinum. In order 

 to lessen the resistance, these points of contact 

 should be covered with cotton moistened with 

 saline solution. If applied for a considerable length of time, these metal elec- 

 trodes become covered with the products of the electrolysis resulting in the course 

 of the passage of the electrical current through this moist conductor, formed by 

 the muscle and nerve tissue. Thus, if a current is conducted through water, a 

 film of bubbles of oxygen eventually accumulates upon the platinum of the 

 positive pole, while the negative pole becomes covered with hydrogen. Presently, 

 the latter assumes a positive change and gives rise to a current which passes in a 

 direction opposite to that of the original current. The final outcome of this is a 

 neutralization of the primary difference in potential. This polarization of the 

 electrodes may be avoided by using so-called non-polarizable electrodes. Those 

 devised by Du-Boid-Raymond consist of zinc terminals immersed in a solution 

 of zinc sulphate. A very simple form may be made by taking two pieces of 

 curved glass tubing, measuring 4 mm. in diameter and about 6 cm. in length. 

 The lower end of each tube is filled with modelling clay or kaolin moistened with 

 normal saline solution. The remaining space in each tube is filled with a satu- 



