The sixth feeling

In the left column evolutionary development of organ of balance in animals is shown. 
For the first time such organs appear at infusorians (fig. 1). Some kinds have bubble with the crystal concretions. At change of position of infusorians the these concretions pressed on one or on other wall of the bubble, allowing to the protozoan to understand, where is a bottom and where is top.

And at more developed organisms a principle of the device of the organs, which allowing to feel the position in relation of a gravitation, remains the same.

The jellyfish (2) has on edge of a body (of the umbrella) cysts with microscopic pebbles - statolith. At an tilting of a umbrella the cyst deviates from a vertical and presses on sensitive fuzz, which be in surrounding him.

At molluscs (3) the statolith - the grain, borrowed from an environment or independently full-grown in organism. Small crystal is concluded in bubble with sensitive fuzz on walls..

The crayfishes (4) have organs of balance at the basis of "moustaches". How the otolith here serves the grain, which should be changed in each moulting.

The vertebrates (5) in addition to bubbles with otolith there is a system of the semicircular channels with a liquid, which flow at movements of a body and it signals about change of position. Here we should do a remark: on drawing is represented the average, conditional organ of balance of the vertebrates. Actually at representatives of different classes he is a little bit various, the some vertebrates have one or two channels instead of three.

In figures 6 - 9 the device of the vestibular apparatus of the person is shown. He is placed in thickness of a temporal bone and represents system from three channels, located in three crossed planes..

Channels are connected with two sacs. All system is filled by a liquid - by the endolymph besides the perilymph be in a narrow crack between the bone and the leathery wall of channels, she amortize all vibrations.

In the sacs so-called sensitive spots lay. It is congestions of jellylike mass, in which are submerged the crystals - otolites. It mass cover the sensitive cages with hairs. Similar cages with hairs are available in three final expansions of channels, so-called ampoules. Here the brushes from it hairs also are stuck together by the jelly-like mass. The sensitive spots of the sacs serve as sensor of position of a head of man concerning a force of gravitation. The otolites through jellylike mass displace in this or other side of the sensitive hairs. It was possible even to measure size of this displacement: at experiments on a centrifuge when artificial weight in 11 times exceeds terrestrial, then the jellylike mass crawl aside on 0,23 mm, however at usual tiltings of a body (for example when the person lays down, passing in a horizontal position) displacement is much less - only 15 microns.

The brushes of hairs serve in ampoules sensors of acceleration. At turns of a head or all body the endolymph in channels by virtue of inertia first lags behind "container". These currents of the endolymph reject brushes. As channels lay in all three planes in which is possible the moving to space and because is available two vestibular organs - left and right, this system allows to reveal any turns and tiltings with the big accuracy!.. Under some data, the vestibular apparatus already responds on turn of the person around of a vertical axis at the special stand with angular acceleration already 0,035 degrees a second for a second.

The person, how and a very many animals has internal "plumb-line". For the first time in evolution he has appeared at infusorians and in the further essentially did not change: probably, the design has appeared successful. As well as in a plumb-line of the bricklayer, here is used light weight, which lay freely or fixed in such a manner what can swing. He is surrounded by the hairs, connected with nerves. At changes of position of a body of an animal the weight presses on the sensitive hairs, and on from what side the hairs perceive this pressing, the central nervous system determines in what side and on how many the axis of a body has deviated from a vertical line (see drawing).
The cargo of the organ of equilibrium we names as "otolith" - in translation with ancient greek «ear pebble». He have such name, because at many lowest animals this device serves not only for the determine of a vertical-line, but also for perception of various vibrations, that is, it is possible to tell, for perception of a sound. The otolith under action of a sound shivers and transmits the fluctuations to cilia. And at the person this system lays in an internal ear, quite near with a hearing aid.
The organ of equilibrium of the person, the so-called vestibular apparatus (he lays before, in "vestibule", of an internal ear), represents system from two sacs and three semicircular channels (exists two such organs, at the left and on the right). The sacs contain jellylike mass, in which exists the microscopic otoliths - crystals of the calcium salts. At change of a direction of a gravitation (for example, at a tilting of a body) this cargo glides inside sac and bends sensitive hairs, which protrude from the wall. Signals about position of jellylike mass with otoliths act continuously and even when her position does not vary: hairs always curved by the weight of the otoliths in one or other side.

The apparatus of the semicircular channels, on the contrary, reacts only on change in position of a body (more precisely, of the head). The channels located in three mutually perpendicular planes, and are filled by a liquid. At rotating of a head the liquid on account of inertia lags behind movement, i.e. born the current of a liquid, which measured by same hairs, such, as already is in sacs.
If the head is motionless or moves with uniform speed, then these receptors of signals do not send, they react only to acceleration.