[8] From the entrails of sheep.
[9] Parker.
[10] “In bowed instruments the wolf occurs owing to defective vibration of one or more notes of the scale. When it occurs, it is generally found, more or less, in every octave and on every string. Different instruments have it in different places: it is most common at, or near, the fourth above the lowest note on the instrument,—in the violin at C, in the violoncello at F. The more sonorous and brilliant the general tone, the more obtrusive it becomes: if the tone be forced, a disagreeable jar is produced. Hence it is idle to attempt to play the wolf down; the player must humor the troublesome note. It is commonly believed that there is a wolf somewhere in all fiddles; and it is certain that it exists in some of the finest, for example in Stradivaris. Probably, however, it is always due to some defect in the construction, or adjustment.
“Violins with a soft, free tone are least liable to it. The cause of the wolf is obscure and probably not uniform: it may result from some excess or defect in the thickness; from unequal elasticity in the wood; from bad proportion or imperfect adjustment of the fittings; or from some defect in the proportions of the air-chamber. In the opinion of violin-makers where it is once established it cannot be radically cured. Some instruments have what may be termed an anti-wolf, i. e. an excess of vibrations on the very notes where the wolf ordinarily occurs.” (Parker).
[11] Lavignac.