204 SPECIAL PHYSIOLOGY. 



The arrangement and position of the tongue are such, that, when at rest, 

 but little or no air can pass through from the wind-tube ; but when a column 

 of air is driven through the latter, the tongue yields in the direction of the 

 attached tube, and an opening is thus established for the outward passage of 

 the air-current. The rapidity with which the tongue at first yielded to the 

 impulse communicated to it, gradually diminishes, because an opening being 

 now established for the escape of the air, it is less exposed to its action. The 

 tongue, by virtue of its elasticity, now counteracts the force of the impulse, 

 and has a tendency to return to its original position ; in so doing, the opening 

 becomes smaller, the backward movement of the tongue momentarily inter- 

 rupts the escape of the air-current, which, now acting with increased power, 

 again causes the tongue to recede : in this manner, a series of more or less 

 rapid oscillations is produced, which throw the column of air in the attached 

 tube into vibrations. The opinion generally entertained is, that the air itself 

 is, in tongued instruments, the primary source of the sound. It is, however, 

 maintained by some that the sounds result from the vibrations of the tongue 

 itself, and that the impulses communicated by it to the air, merely give in- 

 creased power to the sound produced by its own vibrations. 



The pitch of the sound, i. e., the frequency of the vibrations, of an instrument 

 with a rigid tongue, wlien unprovided with an attached tube, is dependent on 

 the elastic strength and length of the tongue. As in the case of elastic rods, 

 the number of vibrations of rigid tongues is inversely as the squares of their 

 length ; thus, a tongu *. six inches long, vibrates four times more rapidly than 

 a tongue, of the same material and equal thickness, twelve inches long. But 

 the pitch of the sound yielded by a rigid tongue, is modified, when an attached 

 tube or body is joined to it ; for the vibrations of the tongue and those of the 

 tube, though they may each produce notes differing widely from each other as 

 regards pitch, yet, when they are connected together, their joint vibrations 

 produce only one sound. The pitch of the note of a rigid tongue is lowered, 

 when the force of the blast is increased. The pitch is never raised by the 

 addition of an attached tube ; moreover, it is not perceptibly modified, so long 

 as the tube is of a moderate length. Gradual lengthening of the tube, however, 

 lowers the pitch ; the rapidity with which this lowering of the pitch takes 

 place, gradually increases with further lengthening of the tube, until, at a cer- 

 tain point, the pitch becomes an octave lower. The tube is now of such a 

 length, that, if air were propelled into it, it would produce the same funda- 

 mental note as the tongue without the tube. If the tube be further lengthened, 

 the pitch of the note is, at first, the same as that of the tongue ; but still fur- 

 ther lengthening of the tube, again lowers the pitch, now, however, only to a 

 fourth ; and so on. 



The action of membranous tongues is, however, of greater immediate inter- 

 est to the physiologist. These tongues, unlike rigid tongues, which, as already 

 stated, behave in their vibrations as elastic rods, vibrate according to the same 

 general law as stretched strings. If one extremity of a short tube be covered 

 by two portions of elastic membrane, or vulcanized India-rubber, in such a 

 manner as to leave a small chink between them, a form of double membranous 

 tongue is obtained, which, in its action, bears a close resemblance to the vocal 

 cords of Man. Sounds are more easily produced by such a double tongue, the 

 narrower the chink ; the size of the latter, however, in no way affects the pitch, 

 which is determined by the length, tension, and thickness of the tongues. The 

 pitch of the note is heightened by touching the tongues with a firm body, a 

 nodal point being then formed. If the two tongues have the same degree of 

 tension, the sound emitted is of a deeper pitch than the fundamental note of 

 either tongue. If they are subject to unequal tension, either one tongue alone 

 is thrown into vibrations ; or if both vibrate together, two different notes may 

 be produced ; or lastly, if they accommodate their vibrations to each other, 

 one sound alone is emitted. The pitch of the notes produced by membranous 

 tongues, either with or without an attached tube, is, moreover, heightened, by 

 increasing the strength of the blast of air ; in this respect, membranous tongues 

 differ essentially from rigid tongues, in which the pitch is somewhat lowered, 

 when the force which throws them into vibrations is increased. The pitch of 

 a membranous tongue, combined with an attached tube, undergoes modifica- 



