508 LEWELLYS F. BARKER 



to elicit the Trousseau phenomenon. Schlesinger also adduces the obser- 

 vation that patients who show a high grade of galvanic excitability of the 

 motor nerves need not necessarily exhibit the Trousseau phenomenon, and 

 the same is true also of the Hoffmann sign. In other words, there is no 

 constant coincidence of the Trousseau phenomenon with either Erb's 

 phenomenon or Hoffmann's. Another important point that may be men- 

 tioned in this connection is the fact that pressure applied to one arm, to 

 produce the Trousseau phenomenon in that arm, may occasionally call 

 forth the Trousseau phenomenon also in the opposite arm ; the contraction 

 in the latter must necessarily be of reflex origin. In any case, the hyper- 

 excitability that is responsible for the Trousseau phenomenon must, on 

 account of the uniformity of the contracture that occurs, correspond to 

 some definitely circumscribed neural mechanism. Neurologists and ex- 

 perimental pharmacologists have done many experiments with the object 

 of determining the localization of the tetany poison in the nervous struc- 

 ture (vide infra), but thus far the progress made in this direction has 

 been very limited. 



Tonic spasms in the lower extremities, also, can sometimes be elicited 

 in tetany by applying a ligature or a cuff around the thigh, so as to 

 compress the underlying structures. The result is, however, less fre- 

 quently positive than in the upper extremities. 



It must not be forgotten that the Trousseau phenomenon may be 

 entirely absent in undoubted cases of tetany. No diagnostician is justi- 

 fied, therefore, in excluding tetany merely by demonstrating the absence 

 of the Trousseau phenomenon. 



Chvostek's Sign 



(The Facial Phenomenon; The Sign of Weiss') 



In tetany the mechanical excitability of the motor nerves is markedly 

 increased, a fact that was discovered by the senior Chvostek (1878). 

 Though this hyper excitability probably exists in all motor domains, it is 

 especially easy to demonstrate, as Chvostek pointed out, by tapping the 

 motor nerves of the face with a small percussion hammer or its handle, 

 or with the tip of the finger. When the mechanical hyperexcitability of 

 the nervus facialis is very pronounced, the mere stroking of the area of 

 skin over the nerve by the tip of the finger will call forth lively contrac- 

 tions in the muscles innervated by it. 



According to the degree of hyperexcitability found to exist, three 

 grades of the facial phenomenon are distinguishable. Thus, in the highest 

 grade (Chvoslek I) a tap in the region of the pes anserinus in front of 

 the ear will cause the muscles of the whole side of the face (muscles of 

 the forehead, eyelids, cheeks, nose, and lips) suddenly to contract. This 



