CHAPTER II.

HEREDITY OF THE SENSORIAL QUALITIES.

PERCEPTION is a fact of mixed nature, at once physiological and mental; it is begun in the organs, is perfected in the consciousness. The soundness of the common opinion which regards our sensations as simple, irreducible, ultimate phenomena, by means of which we know the material world as it is, is extremely doubtful. Setting aside the discussion of this broad question, it is only necessary to say that, taking for their basis physical and physiological discoveries, recent works on psychology-notably those of Bain and Herbert Spencer in England, of Helmholtz and Wundt in Germany, and of Taine in France have shown that sensations supposed to be simple must be dealt with, as chemistry, at its rise, dealt with bodies, also supposed to be simple. These psychologists have shown that neither colours, nor sounds, nor heat, probably, indeed, none of the qualities of the external world, at all resemble the ideas vulgarly entertained with regard to them; that perception is a state of consciousness that corresponds in us to realities external to ourselves, but which does not resemble them : so that this totality of attributes which we call the external world, and which, by a universal illusion, we think we see as it is in reality, is to a great extent the product of our own mind—a creation of which the external world furnishes only the raw material, which our senses then, after their own fashion, work up and complete.

Though we cannot have the slightest hesitation in choosing between these recent theories and the current opinion in regard to the perception of external objects, between that of the Scotch school and of the sensus communis-whose least defect is that it explains nothing; yet, so far as the subject of heredity is concerned, the question has no interest. Whether the material world is perceived immediately as it is, or otherwise than as it is, by a synthesis of consciousness, matters not at all. The only problem we have to solve is whether the perceptive faculties, the modes of sensorial activity, are subject to heredity.

We will observe, in the first place, that, as regards specific qualities, the reply admits of no doubt. If we examine the animal

scale, from the lowest organisms, possessed of no other sense than that of an obtuse, passive touch, up to those most highly sensitive, we see at once that each animal derives a certain number, and a certain kind of senses from its parents. Heredity governs both the quantity and quality of the perceptive faculties, so far as those general characters are concerned which we call specific.

Heredity also governs all that concerns race or variety. Thus, the dog inherits not only a very acute scent, but also the variety of scent which adapts him for hunting a definite kind of game. In the negro the acuteness of this same sense characterizes that variety of the human species.

Doubt, therefore, can arise only with regard to individual differences, and thus our original question is transformed into this: Is the transmission of secondary and individual characters governed by the same heredity which governs the transmission of the perceptive faculties, in their essential and fundamental features? The answer can only be given by facts; we shall see that heredity is usually the rule, even with what is individual, anomalous, and capricious.

We take, then, in order, the five senses as usually accepted. There is now a general agreement to recognize, under the name of vital sense, organic sense, or internal sense, a mode of sensation, without a special organ, diffused over the entire body, and which is, as it were, an internal Touch, whereby we are sensible of what takes place within us. But as this sense is entirely personal, making us acquainted with our own body, and not with the external world, and as it very nearly concerns our pleasures, our pains, our instincts, our passions, we will treat of it in another place, when discussing the modes by which our feelings act, and the heredity of these modes.

I. OF TOUCH.

Touch is the universal, primary sense, possessed by every sentient animal. All the other senses are but a modification of touch, said one of the ancients. Mr. Herbert Spencer has shown how, by evolution and specialization, the other senses-sight, hearing, smell, taste-could have sprung from touch; and how touch

is a universal language into which the other senses, which are special languages, would at first have to be translated in order to be understood. In this fundamental sense, which is at once the most essential and the most material, we distinguish tactile sensations, properly so-called (hardness, softness, elasticity, etc.), and sensations of temperature (heat and cold). Both are governed by heredity.

The extreme difference of tactile sensibility between northern and southern races has often been remarked. Among the latter it is exquisite and refined; among the former, obtuse, or, at least, imperfect. The Lapp, who takes tobacco oil for colic, has a skin as little irritable as his stomach. In Lapland, as Montesquieu puts it, you must flay a man to make him feel.'

It has been observed, says P. Lucas, that parents transmit to their children the most singular perfections and imperfections of touch. There are, probably, in the skin no modes of hyper-æsthesia or of anesthesia that could form an exception to this rule. A woman whose tactile sensibility was so exalted that for her the slightest hurt was an agony, married a man endowed in the highest degree with the opposite quality. He did not lack intelligence, but his heart and his skin were impassible. A daughter was born to them, and she is as insensible to external pain as her father himself. We have seen her endure without complaint, and even without appearing to notice it, pain which would have been very acute for ourselves.

A family from the South, says the same author, who was acquainted with the persons, came to Paris some time ago. Several of the children were born in Paris; but those born there, as well as those brought there from the South, were in childhood extremely sensitive to cold. One of the daughters. married a man from the North, who is insensible to cold, provided it is not excessive. The child born of this union is more sensitive to cold than even its mother; like her, he shivers at the slightest fall of temperature, and so soon as the air becomes cold, he is afraid of leaving the house.

One of the most familiar forms of hyper-æsthesia of the touch is the sensibility to tickling. There are whole families that are insensible to this, while others are so sensible to it that the slightest touch will produce syncope.

Some persons cannot bear the contact or even the near presence of certain objects, such as silk or cork. This morbid sensibility is often transmitted by one or other of the parents. 'We are acquainted with a family, several members of which, both boys and girls, experience instinctively, on touching cork, or the downy skin of a peach, such an internal sensation of shuddering repulsion that the very sight of the fruit is unendurable to them; which, therefore, must be given them with the skin removed.'1

Here we may refer, in passing, to certain hereditary anomalies, such as polydactylism, and the warty membrane of Edward Lambert (of which we have already spoken), both of which cases belong rather to the physiological side of the question.

The hand, which is pre-eminently the organ of touch, is modified by heredity, 'That large hands are inherited by men and women whose ancestors led laborious lives; and that men and women whose descent, for many generations, has been from those unused to manual labour commonly have small hands, are established opinions.' 2

The same is true of left-handed persons. There are families in which the special use of the left hand is hereditary. Girou mentions a family in which the father, the children, and most of the grandchildren were left-handed. One of the latter betrayed its left-handedness from earliest infancy, nor could it be broken of the habit, though the left hand was bound and swathed.

II. OF SIGHT.

Sight is the noblest, the most intellectual, of all the senses, and the most important for science and æsthetics. It is a known fact that accidental blindness may lead to insanity. Congenital blindness certainly influences the mind: the imagination of one born blind, which possesses only tactile sensations, cannot be anything like ours, in which visual sensations predominate. Hence, from a purely psychological point of view, the heredity of the sensorial modes of vision is worth studying.

The individual varieties of this sense may be classed under three heads, accordingly as they depend on mechanical causes, or

1 Lucas, i. 481.

2 Spencer, Biology, vol. i. § 82.

on anæsthesia or hyper-æsthesia of the nervous element. anomalies are transmissible by heredity.

All

1. The peculiarities of vision which depend on mechanical causes are strabismus, myopia, and presbyopia. The transmission of these is very common. In general, it is to hereditary causes that we are indebted for the conformation of our visual apparatus, and, consequently, for our being far or near-sighted.

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Portal, in his Considérations sur les Maladies de Famille, describes an imperfect form of strabismus, called the Montmorency sight, with which nearly all the members of that family were affected.

Darwin observed that the Fuegians, when on board his ship, could see distant objects far more distinctly than the English sailors, notwithstanding their long practice.1 This is clearly an acquired faculty, accumulated and fixed by heredity.

One of the most striking cases of heredity of vision is the ever increasing number of the myopic among persons given to intellectual work. According to M. Giraud Teulon, continual application with the eyes near the object is the great cause of myopia. Professor Donders, of Utrecht, while studying the statistical reports, was surprised to find that myopia is a disease of the wealthy classes, and that the inhabitants of cities are specially liable to it, while those of the country are almost exempt. In France the Conseils de Révision have noticed the same fact. In England, at the Chelsea Military School, among 1,300 boys only three were myopic. In the Universities of Oxford and Cambridge, however, the number of myopic subjects was considerable—at Oxford 32 in 127. In Germany the results are even more decisive. Dr. Colin, of Breslau, undertook the task of examining, in the schools of his own country, the eyes of 10,000 scholars or students. Among these he found 1,004 myopic-about ten per cent. In village schools they are not numerous-only a quarter per cent. In the town schools the number of the myopic increases with the grade-primary schools it is 67; middle schools, 10'3; normal schools, 197; gymnasia and universities, 26°2 per cent.

1 Variation, etc., ii. p. 223.

2 Revue des Cours Scientifiques. 3 Sept. 1870.