140 NERVE FOECE. CHAP. XI. §. U. 



the electrodes come in contact with heterogeneous parts 

 of the nerve, during nerve action or not, then current 

 force is manifested ; this effect being, however, the result 

 of the so-called nerve current. 



Sect. II. The Galvanoscopie Frog. 



The galvanoscopie frog is, unfortunately, accom- 

 panied with great uncertainty in its indications, and 

 consequently requires the greatest care in its em- 

 ployment. The delicacy of its indications does not 

 always correspond with its freshness; the muscles 

 may he easily excited to contract when first prepared, 

 but immediately afterwards it may be difiBcult, or 

 even impossible, to arouse the contractions. This 

 difficulty may arise from the muscles having once 

 contracted remaining so. Again, a limb which is 

 not very delicate in its indications at first, may, 

 after some little time, be aU at ■ once seized with 

 slight tetanic contractions ; this circumstance may 

 arise from the nerve becoming dry, as has been 

 abeady pointed out by Marshall Hall*. There 

 are other circumstances which are undoubtedly in- 

 fluential, and amongst them the vital condition of 

 the animal. It has frequently happened to me, that 

 a limb which has been laid aside as worthless, has 

 subsequently proved upon trial to be most delicate 

 in its indications, without my being able to account 

 for it. The muscles should be neither flabby nor 

 too much contracted. The only test to be relied 

 '' Edinburgh New Philosophical Journal, April, 1848. 



