Popular Science Monthly/Volume 62/February 1903/The Behaviour of Blind Animals
|THE BEHAVIOUR OF BLIND ANIMALS.|
By Professor WESLEY MILLS, M.A.. M.D.,
MCGILL UNIVERSITY, MONTREAL.
IN the course of years I have had the opportunity of observing a considerable number of animals totally blind in either one or both eyes and to these only shall I refer in this paper.
Pigeons.—All those observed, that were otherwise normal, have been blind on one side only. The defect does not seem to have resulted in any great inconvenience or disadvantage to the individual. Birds do not, it is likely, possess binocular vision, in the sense in which the term may be applied to many mammals; and in consequence of the defect, cutting off the field of vision on one side completely, the bird endeavors to make up for this by adaptive movements of the head, which it can bring about with a facility not possible to the mammal.
It also, through experience, becomes more alert than the average pigeon; nevertheless, when the struggle for existence becomes keen, as for example when a limited quantity of food is strewn about, it is shown to be plainly at a disadvantage, both in securing the food and in the bodily conflicts that are apt to arise between it and its competitors.
White Rats.—I have observed several white rats, some of which were blind in only one eye, others in both. The results were in some respects very different from what might have been expected, and in this the difference between the bird and the rabbit, on the one hand, and the rat, on the other, was striking.
Even in the case of total blindness, the rat is not handicapped as one might suppose must be the case. In a very few days the rat blind in only one eye seems to ordinary observation to be in no appreciable degree worse off than his fellows. In a short time the specimen, totally blind, moves about so well that one would need to look carefully to be assured that he gets no assistance from the visual sense. But in his case there are times when it is evident that he is handicapped. In exploring new surroundings he proceeds with special caution, stretching out his neck, sometimes resting on his hind legs, more frequently elevating his fore parts and sniffing in an unusual way, showing an extreme care and plainly making use of his acquired greater facility, or perhaps one should say, his accustomed and habitual greater use of senses that normally are not required to function to such a marked degree.
He is also somewhat more timid and retreats in the way rats do toward their place of exit, with greater readiness. He is of course more at the mercy of his enemies, and yet not to the degree one might have supposed on account of his greater caution as well as the fact that his senses of touch and smell make up so fully for the lack of sight. It must be borne in mind that the olfactory tracts of the central nervous system in the rat are highly developed and their association-paths numerous, so that in an eminent degree the rodent, and especially the rat, is worked, so to speak, as an entire mechanism largely through the reflex paths of smell.
One of the unexpected results of sudden blindness in the case of white rats, whether affecting one or both eyes, was a most marked alteration in disposition. Eats that were perfectly tame became at once ferocious; it was unsafe any longer to attempt to handle them as formerly, or to remove anything from their cage, for in an instant they seemed aware of the approach of one's hand and were not only ready but able to pounce upon it at once; even metal forceps were seized by the teeth. After a considerable period in a rat blind in both eyes this ferocity disappeared, but not so, or to but a slight extent, in those lacking the power of vision on only one side.
In our experience in the breeding of white rats, it is rare for the female to devour her young, but invariably have those blind white rats killed and eaten to a greater or less extent every litter they have had, though placed under circumstances exactly similar to those of the intact rats.
Rabbits.—My opportunities to observe this species of rodent when blindness was found on one or both sides, has been almost as good as in the case of the rat. The differences noted in the animals is considerable. A rabbit totally blind behaves in general much like a rat similarly defective, but he shows less tendency on occasion to retreat towards his place of safety, is less alert and apparently less prepared to meet emergencies. But the readiness with which he manages to avoid obstacles in his path is striking. He also, like the rat, stretches out his neck, rises sometimes on his hind legs, but more frequently raises the fore parts of his body into the air, all with the obvious purpose of exploring the nature of his environment to a degree and with a frequency not witnessed in the normal rabbit. Such an animal is, however, more likely to fall under the power of his enemies than is the rat, though so long as food is plenty near his burrow the wild animal would no doubt develop that caution and use his other senses to such an extent that he would generally escape; but that he would in the long run fall a prey to some wily fox seems more than probable.
I have noticed no change in disposition in the case of the rabbit akin to that in the rat and none of the blind specimens has had young.
Neither the rabbits nor the rats ever make the mistake of walking off a place elevated above terra firma. As I have elsewhere pointed out, this tendency seems to be a fundamental instinct manifested by even the youngest mammals and is evidently of vital importance for their preservation.
Cat.—The cat on which I am able to report was not in good condition after she became suddenly blind in both eyes, and lived but a few days, or I should have been able to note more fully whether her psychic state had been modified by experience.
When put down on the floor she moved about in a slow and apparently cautious way, and, though plainly perfectly blind, when she came near objects she touched them only slightly. In this the whiskers evidently served a good purpose, as was also observed in the rodents. When one made a noise on the floor as by tramping with the feet, puss invariably moved towards the sound, and so perfectly that by walking about one could cause her to describe complicated figures, from which and other observations I conclude that she had become a mere reflex mechanism worked by the most prominent stimuli of the moment from the external world. When she came to a wall, and especially a corner, she stopped and sometimes lay down—showing that the 'puss in the corner' tendency has a deep foundation, for I am inclined to believe that this animal was not conscious in the true sense of the term. This cat had become blind owing to a hemorrhage into the optic thalamus of the brain and lived but a few days afterwards.
I have not reported any other cases in this paper in which there were brain lesions, the discussion being too complicated for my present purpose. That the cat was guided purely reflexly by sounds was evident from the fact that when one stood on a table and tramped as before, puss underneath the table was soon brought to a standstill just below the source of the sounds. Such a remarkable case of guidance reflexly by the ear I had not seen before, and it proved very instructive to me.
Dog.—Of the blind dogs I have observed I shall refer to but one. He was a cross-bred skye terrier and formed one of a litter kept in a room in the college basement. He became totally blind when between two and three months old. After this he soon changed greatly in disposition; he, like the rats, seemed to revert to a sort of feral condition. He would on the entrance of any one into the room hide, and when approached would bite savagely at the extended hand; in fact, in order to catch him it was necessary to throw a sack or some such object over him. He had gnawed away the legs on which Ms cage stood and to which he was chained for a time.
This dog seemed to be at least equal in intelligence to the other members of the litter, his companions. So far as the objects in the room that had a stable situation were concerned, he was perfectly oriented, but if a new object was laid down he would run against it and then attack it as savagely as he would one of his fellows who came in his way.
If any stranger came to the door of the room he seemed to know instantly and would bark fiercely, but he never did this when the regular attendant entered, however silently he approached, being guided probably largely, but by no means wholly, by the sense of smell. He was by far more alert than any of his companions and seemed to be put into a state of high tension by the slightest stimulus.
This dog had a ravenous appetite, and when the vessel containing food for all the dogs of this litter was put down he was generally the first to reach it, though at the moment he might possibly be in the most distant part of the room, and certainly he did not come off second best in the struggle.
He was so like a wild animal, was of so bad a temper, and altogether so undesirable a creature, I thought it best to chloroform him at the end of a few weeks.