chap, xv.} ELECTRICITY IN DIAGNOSIS. 163 



these facts. The explanation offered by Erb and 

 corroborated by Ziemssen is that nerve and muscle 

 respond differently to the electric current, that, 

 while the nerve responds readily to currents of very 

 short duration, like the induced, muscle responds 

 more to currents of longer duration, such as are ob- 

 tained by interruptions of the constant current. 

 Consequently, when the irritability of nerve and 

 muscle to faradisation has disappeared, the response of 

 the latter to galvanism may still be elicited. In time, 

 however, if the degeneration proceeds, galvanism will 

 also fail to elicit contraction of muscle. The cases 

 which show these DEGENERATIVE REACTIONS, as they 

 are called, are rheumatic paralysis, facial palsy (due, 

 e.g., to cold, i.e. not hemiplegia), lead palsy, paralysis 

 due to injury of nerve trunks, and others. To sum up, 

 then, in central paralysis irritability is unaffected, 

 in peripheral paralysis irritability rapidly disappears, 

 but in some cases irritability of the muscle to gal- 

 vanism is increased, and thereafter disappears. 



(3) To detect foreign metallic bodies, e.g. a bullet, 

 in the tissues, the constant current is employed. 

 What is required is a battery sufficiently powerful to 

 ring an alarm bell, and in the same circuit a probe of 

 particular construction. The probe should be of in- 

 sulating material, having imbedded in it, and insulated 

 from one another, two copper wires. The ends of the 

 two wires are exposed at the end of the probe. If 

 these wires are put in the circuit of the battery and 

 bell, the bell will not ring, because contact is broken 

 between the two wires. If, however, the probe be 

 pushed into a wound and come in contact with a 

 bullet, then, both wires touching the lead, the circuit 

 is completed, and the ringing of the bell gives the 

 indication. Instead of a bell, a galvanometer may be 

 used (not one of sensitive construction), its deflection 

 intimating metallic contact. 



