The sensory effect of local application of hypertonic salt solutions

Abstract

While engaged in an investigation of certain effects of local application of salt solutions to exposed nerve trunks, and to nerve terminations exposed by abrading the skin, a paper appeared by Wiki, 1 in which results are presented and interpreted as showing that local anesthesia followed intracutaneous injections of solutions of various substances into guinea-pigs. A number of the salts employed by him were included among those used by us. Since the interpretation of an anesthetic action by him is at such variance with our results, it seems advisable to make a brief statement at this time.

Wiki states that strong solutions of magnesium chloride or sulphate when injected intracutaneously in the back of a guinea-pig produce marked anesthesia, as evidenced by decreased reflexes upon stimulating the affected skin area; while in our experiments, direct application of strong solutions of these salts to exposed nerve trunks (frog and turtle), abraded skin areas (human), or to the unabraded skin (frog), have resulted in very positive evidence of an irritant action. In the case of nerve trunks thoroughly isolated from surrounding tissue, a block may be produced by keeping the nerve bathed in a strong solution; but in the case of application to abraded or unabraded skin, though such applications have been continuously applied for twenty minutes or more, not one symptom of anesthetic action could be detected. A number of other solutions and substances were tested in the same way and all, with the exception of cocain, gave similar results, the only difference being either a difference in the time of onset of evidence of irritant action or in the degree of such action.

Among the substances investigated by application to abraded skin areas, magnesium salts were among those that gave rise to very severely painful sensations which persisted for twenty minutes or more, at which time the solutions were removed.