SENSE OF POSITION IN ANIMALS

Dominion, Volume 21, Issue 84, 7 January 1928, Page 22

SENSE OF POSITION IN ANIMALS

HOW THEY KEEP THEIR EQUILIBRIUM

If airmen depended on the same mechanism as rabbits do for keeping themselves right-side-up, they would not run the risk of flying upside-down in a fog in ignorance of the fact that their machine had turned over. This was one of the most interesting deductions to be drawn from the public lecture delivered by Professor A. J. Hall at University College on some of the work of the late Professor Magnus, of Utrecht (says the “Morning Post”). He pointed out that in animals lower than the rabbit the sense of position in space was largely determined through the labyrinth of the ear, whereas in the case of higher animals such as the cat, dog, ape, and man there was more and more dependence placed on the eye. As a boy, the lecturer said, he had learnt that the proper thing to do if a horse fell was to sit -bn its head and wait for assistance, while anyone who

had bad his own head sat upon must have found himself in a very helpless condition. A manifestation of this tendency to keep right side up was seen in the hospital wards when a patient was awakened, the instinct being for the patient to place the head in an upright posture.

The whole mechanism had been very carefully studied by Professor Rudolph Magnus, who had built a wonderful superstructure on the foundations so brilliantly laid by Sir Charles Sherrington. , The main object of the researches conducted by Magnus had been to discover the nervous mechanism which had made it possible for an animal to determine its position in space, to get right side up, and to keep so. In the case of an animal whose spinal cord was severed below the brain it was impossible for it to stand up, but if the cut was made through a portion of the medulla it could stand.

Magnus's work had started from the observation that if such an animal was laid on its side and its head was turned there was a'difference in the muscular tone of the two sides of the body. When the animal was right side up the limbs were not stretched, but they were stretched to their utmost when it was placed upside down. This, when the head was fixed, was due to the stimuli received from the labyrinths of the ears, for if they were removed there was no alteration in muscular tone. If the head was free to move on the trunk and the labyrinths were destroyed other reflexes came into action, and as the head was turned there was bending or stretching of certain of the limbs. If a cat bent its head to look down to its food it automatically bent its forepaws ; if it raised its head it stretched its forepaws. If the animal was placed on its back it stretched its legs, perhaps as a means of protection. The clue as to how an animal tended to right itself had been given by its behaviour as it came out of an anesthetic. On being stimulated by pinching its tail, it rotated its head towards the normal position; at a later stage this was followed by a rotation of the upper part of the chest, and finally the hindquarters were brought lound, and with .a jerk it came into normal position.

It was essential for the animal that it should get>its head straight, but it only did so if tlie labyrinths were intact. An animal could, however, get up even if the labyrinths were destroyed, as reflex stimuli could be sent from the neck, or from the body surface to the head, or even in emergencies from the body surface acting on the body itself. Professor Hall showed a number of slow-motion pictures illustrating how the body of an animal, such as a fowl or a duck, could be turned through 180 deg. while its head remained in correct position as if held in a vice.