Lectures on nervous diseases from the standpoint of cerebral and spinal localization, and the later methods employed in the diagnosis and treatment of these affections . her (using that formof cell for example), and continue to do so throughout the entire series ofcells (Fig. 138), we have formed what is known as a ??compound circuitor an arrangement in series. If we join all the negative or carbonelements together, and then the positive or zinc elements in a similar way,we have what is known as a simple circuit (Fig. 141). Finally, we maydivide the cells into gronpis; then join those of each
Lectures on nervous diseases from the standpoint of cerebral and spinal localization, and the later methods employed in the diagnosis and treatment of these affections . her (using that formof cell for example), and continue to do so throughout the entire series ofcells (Fig. 138), we have formed what is known as a ??compound circuitor an arrangement in series. If we join all the negative or carbonelements together, and then the positive or zinc elements in a similar way,we have what is known as a simple circuit (Fig. 141). Finally, we maydivide the cells into gronpis; then join those of each group in simplecircuit; and afterward unite these groups as if they were single cells. Now, what will the effect of each of these methods of combinationhave on the intensity of the current? Ohms law comes into play indeciding such a problem. 620 LECTUKES ON NEllVOUS DISEASES. We must (iist ascertain tlie internal resistance of the form of cellwhich we have selected for our battery.* We must know also theexternal resistance which we shall have to overcome in our proposeduse of it. Finally, we must ascertain the electro-motive force of theelements of each Fig. 139.—A Schematic Repkesentation op the Introduction of a Human Body (a)INTO THE Circuit of Closure op a Galvanic Chain. (After Erb.) +=the anode;— = the cathode. Suppose, for example, that E = l,Ir —20, Er=10. The currentof each cell would then be expressed as follows :— 1 1 C = = —= .033+. 20+10 30 * To computo the internal resistance of a cell or battery requires apparatus not erener-ally owned by medical practitioners, , a coil rheostat, which may be confidentlyregarded as accurate, and a carefully calibrated galvanometer, by a standard maker. Therule given by De Watteville, and copied from him, apparently, by Aniidon, would be simpleif it were true. I have tested it again and again, and have personally discarded it usunworthy of credence. I have also had a professional electrician test it. He arrive
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