604 LEWELLYS F. BARKER 



tetany, it was Erb of Heidelberg who first taught us that one can definitely 

 demonstrate this galvanic hyperexcitability and make use of it as a diag- 

 nostic test. He showed also how the contraction formula alters, and he 

 emphasized the relatively early appearance of an anodal closure tetanus 

 and of a kathodal opening tetanus. Since he made his studies, increased 

 electrical excitability of the motor nerves in tetany has been known as 

 "Erb's phenomenon." 



Progress in the quantitative measurement of the changes in the electri- 

 cal excitability of the motor nerves in tetany was made by N. Weiss (a.) 

 (b) and especially by von Frankl-Hochwart (1886). Thus, these observers 

 demonstrated that muscular contractions occur only on kathodal closure 

 in normal adults in the domain of the nervus ulnaris when that nerve is 

 stimulated with a galvanic current of 0.9 to 3.3 milliamperes, whereas in 

 patients suffering from tetany, contractions will result from the applica- 

 tion of a current of the strength of from 0.1 to 0.7 milliampere. 



It was soon found that this hyperexcitability of the motor nerves to 

 galvanic stimulation is one of the most constant and important symptoms 

 of tetany. Escherich has emphasized its especial helpfulness in the diag- 

 nosis of tetany in children. In his opinion, it is the most important of 

 all the signs for diagnosis, and this view is now held by most pediatrists. 



A practical article, very valuable to clinicians who actually apply the 

 galvanic tests, is that of Mann (1900) who collaborated with Thiemich. 

 Mann's conclusions are as follows : 



1. For the demonstration of the increase of electrical excitability of 

 the motor nerves in tetany, the examination of a single nerve, namely the 

 nervus medianus, is entirely sufficient. 



2. If the kathodal closure contraction (KCC) appears when the 

 nervus medianus is stimulated with currents below 0.7 Ma. in strength, 

 there exists an increase of excitability. If the threshold lies above this, 

 an increase of excitability may still exist, though in that event one can- 

 not come to a definite conclusion by testing for the kathodal closure con- 

 traction alone. 



3. An increase in electrical excitability can be determined with cer- 

 tainty by studying the behavior of the kathodal opening contraction 

 (KOC). This contraction appears in all cases of tetany on the appli- 

 cation of currents below 5.0 milliamperes (usually much lower) in 

 strength, whereas, to produce this contraction in normal persons much 

 stronger currents are required. 



4. Whereas, further, the anodal closure contraction (AGO) consid- 

 erably predominates in the majority of normal persons over the anodal 

 opening contraction (AGO), it is very common in tetany (though not 

 entirely constant) to find the anodal opening contraction greater than, or 

 equal to, the anodal closure contraction ; or, at any rate, the strength of 

 the currents for the anodal closure contraction and the anodal opening 



