The Collaborative International Dictionary of English v.0.48:

Syntonin \Syn"to*nin\, n. [Cf. Gr. ? stretched tight, intense.]
   (Physiol. Chem.)
   A proteid substance (acid albumin) formed from the albuminous
   matter of muscle by the action of dilute acids; -- formerly
   called musculin. See Acid albumin, under Albumin.
   [1913 Webster]