About ten years ago I began an investiga­tion into the results of the applica­tion by man to the domestic horse of various forms of harness, desiring to find out if these results were capable of being transmitted from one genera­tion to another. In 1908 I had not got very far, but thought it well to bring before the Zoological Society of London the results observed up to that time and read a paper entitled, “Some observations on the effects of Pressure upon the Direction of Hair in Mammals.” It was kindly received, but was not published in their proceedings, as it appeared to the Publica­tion Committee a paper more suited to “another place,” presumably those of a veterinary society. It was illustrated by the two figures I give here of a horse in full harness, and another with the chief results as to changes of the direction of hair, or new patterns, displayed on its coat.

Progress of Inquiry.

Being disposed to think that the investiga­tion could be carried further, I proceeded to look about for any examples in horses which might show the transmission of these artificial results to their descendants, and had to wait awhile before I could see which of the regions affected by the pressure of harness were likely to afford the required phenomena. These were in due time forthcoming, and will form the chief subject of the present chapter. I look upon them as cases of an undesigned experiment and will describe them later.

In the present stage of science all hypotheses must be submitted to the test of experiment before they can enter the charmed circle of natural laws. For this reason one must endeavour to apply the test of experiment to the hypothesis before us.

The Nature of Experiment.

Hitherto I have gone no further than the region of experience and observa­tion, from which, Jevons says, “all knowledge proceeds.” There has been abundance of observa­tion of phenomena in this quest and I have ventured even on hypothesis. Experiment is shortly defined by Jevons as observa­tion plus altera­tion of conditions. He points out that when we make an experiment we more or less influence the events which we observe, as when we bring together certain substances under various conditions of temperature, pressure, electric disturbance or chemical action and so on, and then record the changes observed; and, that experiment may be of two kinds, experiments of simple fact and experiments of quantity. It is unnecessary here to describe all the rigorous rules that the man of science so rightly imposes upon himself before he claims to have proved his hypothesis, merely adding that among others he requires, Exclusion of Indifferent Circumstances, Simplifica­tion of Experiments, Removal of Usual Conditions, Removal of Interference of Unsuspected Conditions, Blind or Test Experiments, Negative Results of Experiment, and he lays down the limits of experiment. Those who have not for themselves investigated some scientific problem may learn from this statement some of the difficulties of the work of scientific men and will not fail to respect and admire the caution, patience and honesty of the scientific worker, and will perhaps feel the more gratitude to a class of men by whose self-denying labours they live and move and have their being in a modern state, and by whose discoveries, thus established, they are frequently preserved from premature death.

Experiments for the Present Purpose.

Now in the matter of experiment for the proof of the thesis that changes in the habits of an animal cause the changes observed in their hair, it is at once seen that, ex hypothesi, no one can impose and work with such calculated conditions as are ordained by experiment, strictly so-called. The action of a habit is a slow process and the movement of a hair is slow; moreover the lifetime of a man is too short and that of a horse, for example, too long to allow of any individual experimenter applying artificial pressure through many generations of horses, so as to be able to verify his assertion that the effects of artificial pressure do what is claimed, and that these effects are transmitted from one genera­tion of horses to another. One can conceive a calculated experiment of the kind made with numerous individual rats, and successive generations, but it is hardly likely that effectual pressure could be applied to the hairy coats of such small and elusive mammals as would serve to test the hypothesis.

Undesigned Experiments.

We are thrown back, then, on such experiments as may be provided for us by the uncalculated operations of man through many ages. This class I call undesigned experiments and have had more to say about numerous examples of these in another place.57 Using the term experiment broadly we see many occurrences which consist in an accidental observa­tion of a fact, and Jevons mentions five of these which have led to organised results in science—the double refrac­tion in Iceland spar by Erasmus Bartholinus, the twitching of a frog’s leg under stimuli by Galvani, the light reflected from distant windows with a double-refracting substance by Malus, the form of a vertebra by Oken, and the peculiar appearance of a solution of quinine by Sir John Herschel. But he notes something further than this, that is, the way in which astronomers make the earth’s orbit the basis of a well-arranged natural experiment. He says further that “Nature has made no experiment at all for us within historical times” among animals living in a state of nature, allowing at the same time that man has made an approach to experiment in his domestica­tion of many animals. Huxley himself kept an open mind until the last as to the validity of Natural Selection in the Origin of Species, because of the fact that races which are sterile together have not yet been produced by human cultiva­tion, for example, the sterility of mules, the human product of the jackass and the mare. I allude to this to show that such a result, if effected, would have constituted a valuable experiment in biology in favour of Natural Selection.

Harness on Horses.

Man has, however, been carrying on unconsciously throughout a great stretch of time an experiment upon the hair on the coat of a horse by the use of harness. This is an old story and its rudiments are mentioned by Professor Scott Elliott.58 He states that the men of Cromagnon are believed by a high authority as to their rock-paintings to have depicted some marks which represent rude harness of some kind, though he himself expresses doubt on the matter. He also quotes the same authority for the figures made by the Madelenians as having found signs which can be interpreted as halters or even bridles. Be this as it may, we need not carry our search for the use of harness to this hoary antiquity, but know well from history that for many thousands of years man has been employing harness on his friend and servant, thus making the essential conditions for an experiment of which he and his servant were alike unconscious, that is to say, he influenced a growing living structure, the horse’s hair, by the artificial force of pressure, applied to the coat at various points. These varied from age to age as to fashion and material, and the present full development of harness of a draught horse was probably slow in coming.

Examples of the Effects of Pressure.

Looking at the figures of a horse harnessed, and another without harness, Figs.49 and 50, one sees on the latter eight different regions where patterns of hair, not found in the horse normally, are displayed. They are as follows:—

All these aberrations from the normal are rare except the first (A), and all are based on the observa­tion and drawing of individual specimens which I brought before the Zoological Society and the details of which are given in a note on page129. The rarer seven examples are described because taken together they show what the pressure of harness can do at certain points where its pressure is adequate, and they are all situated where they might be expected if such a force could effect hair-changes, and there are none of them found on areas where neither pressure nor underlying muscular traction can act efficiently. Thus in many thousands of horses I have never seen a hair-pattern on the middle of the flank or the under surface of the abdomen or the middle of the back or gluteal region or on the fore or hind legs. This negative evidence is of great importance, and must be taken for what it is worth. I may venture to remind the reader that every one of these phenomena is an artificial product of man’s treatment of the horse. They come thus under the category of undesigned experiments.

The only one of the eight artificial patterns, which as a rule are in the form of a whorl feathering and crest, that needs, further close attention is the pattern A, produced on the under surface of the horse’s neck by the collar, and this will be examined separately.

The Selected Example—Ventral Surface of Horse’s Neck.

If I set out to convince a doubting opponent that these things are as I assert, three conditions may at once be laid down. First, it must be shown that the patterns found here are not part of a normal arrangement. Second, that they are produced by pressure of the harness. Third, that examples of them be forthcoming in young horses never exposed to the action of harness.

First. The normal arrangement of hair on the under surface of the horse’s neck shows an even stream passing from the head to the chest, where it is interrupted by the pectoral patterns, and during that course resembles precisely the other normal streams in this and other mammals.

The opponent asks, “How do you know this is the normal slope, and that the patterns you describe are not normal, and what you describe as normal is not a variation?” This is a perfectly proper and timely question and can only be answered fully by examina­tion of and noting a large number of draught horses.

The Normal Arrangement on the Ventral Surface of the Horse’s Neck.

This examination has been made in a number of specimens large enough to satisfy the most exacting opponent. In all, 748 were examined as to the hair on the under surface of the neck and 338 of these presented the normal arrangement and 411 showed patterns of various kinds ranging from a trifling reversed area two to three inches long on one side of the middle line, to a finely-formed whorl, feathering and crest occupying the whole of the surface where the collar is able to reach. These two limits are shown side by side in the figures. I should add that among the 411 which I term abnormal, for the sake of clear contrast, the number of varieties of pattern were numerous and bewildering.

Cart Horses.

A very significant result followed from a special examina­tion of 300 cart horses, as distinguished from hackneys. These showed the astonishing number of 277 specimens of what I call the abnormal and only 23 of the normal type. This special group in no way weakens the force of the larger study of 748, for the 300 cart horses are included in it, and, if removed, would have left the normal specimens in the hackney or general group very much more numerous. Looking at the cart horses, which are specimens of a highly-specialised breed for heavy draught purposes, one may assert with some confidence that, for them, the normal pattern of the hackney is becoming their abnormal. It must be remembered that these great creatures with large muscular necks are during most of their time of work pulling hard against the collar, and the very conditions required for making patterns of hair through pressure of harness are present in a remarkable degree. It is indeed an undesigned experiment within an experiment.

Analogy.

In addition to these statistics which may be taken as conclusive on this question of the normal arrangement, I must point out that it is against all reason, and analogy from all other mammals, to doubt that the normal arrangement is as I describe it. No hair-clad mammal either within the family of the EquidÆ, or without, has any other arrangement on the under surface of its neck than what is here shown to be the normal one—a uniform uninterrupted slope from the head to the chest. There is also a feature of this greatly variegated piece of the horse’s coat under its neck, and that is that it is so highly variegated with diversity of pattern as to make it unlike any normal or natural structure or character in any animal. That is not the way Nature does her normal work. It would be impossible to give illustrations of many of the patterns here found, though I have notes and sketches of a large number taken from the examina­tion of thousands of specimens; so I have selected eight (Figs.51, 52, 53, 54, 55, 56, 57 and 58) of the best representatives of these and the details of each are given under each figure.

Effects of Pressure by Harness.

Second.—The next stage of the inquiry demands that one should show the patterns to be due to pressure.

In the accompanying drawings the under surface of the neck and the chest of each horse is shown with the collar in place, the centre portion of which is cut out so as to show the arrangement of hair beneath, and some of the varieties are seen to extend for several inches above it. In considering this process one ought to watch the way in which the collar of a horse, as a rule, is seen to move up and down as he trots, for in most cases, except in cart-horses, the collar fits very loosely and is easily jolted upwards. This will explain why the patterns often extend upwards above the proper position of the collar, but it must also be remembered that never have I found a pattern higher up in the middle of the neck than a loose collar can reach when jolted. (Close to the lower jaw there is a whorl or pattern often found which belongs to a different category, and is not to be confused with the patterns in question.)

In the conditions described there is present exactly that frequent pressure of a moving body against the growing hair, which is requisite to produce changes in its direction, as well as the more fixed pressure of the collar when it is fitting firmly against the lower part of the neck.

By way of confirma­tion of the view that this is the modus operandi one has only to point to the other seven regions shown in Figs.49 and 50, in which the connec­tion between the pressure of harness and the produc­tion of a new pattern is beyond all doubt one of cause and effect.

The Proof of Transmission of Pattern.

Third.—To show that the effects produced by pressure in one genera­tion are sometimes inherited by its descendants it is necessary to examine a few examples of young horses who have never borne the yoke as yet.

I examined some mares of the farm-horse type with their foals in a field at Radley in 1915 with the following results. All the mothers showed the common reversed area or pattern on the under surfaces of their necks. Of the five foals all but one showed clear evidence, even in their thick young coats, of a similar pattern, the fifth had none. I also noted two similar examples in a field at Harrogate in the same year and both the mothers and the foals showed the usual pattern; and again at Radley in 1918 four more foals, one of them 24 hours old, who all showed this reversed area. Here then are ten examples of undoubted transmission of the effects of pressure by harness in subjects so young as to be still suckled by their dams, and, of course, never themselves touched by such pressure. I submit that even one such unmistakable example would be enough to prove the case, and that the necessary conditions of a rigorous undesigned experiment by man have been fulfilled.

Objections.

At the end of this chapter which concludes the facts of the case I think it may serve to make the position a little clearer if I state objections which have been or might be raised.

It will not escape the mind of any person who has followed critically this process of inquiry, that in Chapter VII, where the immense variety of the patterns found on the side of the horse’s neck are described, there is an apparent resemblance between them and those on the ventral or under surface of the neck. The former were shown to be due to natural forces, those of sustained and repeated underlying muscular traction of muscles and jolting of the neck in locomo­tion; whereas in this chapter a considerable number of patterns have been brought forward and pictured on the under surface, and these are attributed to artificial pressure from harness. The reasonable objection is raised, “Why should the former be considered natural and the latter artificial in their origin?”

The answer to this is supplied by a considera­tion of the muscles shown in the two contrasted regions. In Figs.3, 4 and 5, the muscles of the side of the neck are shown to be remarkably strong and numerous (in three layers), and diverging in their directions. In the muscles of the under surface of the neck of the horse, see Fig.12, the muscles of the two sides shown are nearly parallel and no conflict of opposing or diverging muscles can well take place in this “debateable land.” If there were much divergent or opposing action going on it would, of course, produce the effects on the hair towards the upper part of the neck, where the muscles tend to diverge more and more as they pass to the head, and I have stated above that not a single instance in many thousands of horses has been found above the level where a loose collar ceases to rub when jolted upwards. This is very conclusive on the matter of diverging or opposing muscular action.

Then again the jolting in locomo­tion, which, in the case of the side of the neck is probably more effectual in producing changes of hair than even muscular traction, is almost absent from the under surfaces, as can be learned from careful watching of the motion of a horse.

Another reason which meets this objection very fully is that I have shown that 300 cart horses presented 277 of their number with reversed areas of patterns in the middle line of the under surface of the neck and these thick-necked animals are just those in which the collar is closely applied to the front of the neck in their heavy draught work, thus rubbing almost incessantly against the lie of the hair. In the thinner necks of the hackneys there are comparatively few indeed of the patterns found here and their collars as a rule fit very loosely and badly, and these frequently show a jolting up and down clear of the neck, which is seldom if ever present in a well-formed cart horse.

Further proof of this is shown by the simple fact that it is under the collar and within its range of movement that the changes of hair are produced.

No artificial pressure such as that of a collar is exerted on the parts of the side of the neck where the patterns are found; so I would submit that these two selected and much-disturbed areas owe their hair-patterns to two wholly different forms of mechanical cause.

I referred in the Preface to an important criticism of my earlier book on The Direction of Hair in Animals and Man, and will now treat this in some degree of detail. It is from the pen of an eminent American biologist, then Miss Inez L. Whipple,59 now Mrs. Wilder Harris, and it is a careful, independent and thoughtful contribu­tion from one who by her studies in this field and in the study of the mammalian palm and sole is widely known, and as widely respected.

Miss Whipple refers on page403 to certain whorls and featherings on the backs of the lion, ox, giraffe and larger antelopes, which I then attributed to the action of the panniculus carnosus in shaking off flies. I am free to confess that the action then invoked by me was inadequate and incorrect and the explanations now given of them in Chapters X. and XI. on the ox and the lion, I think, are less open to criticism.

Again on page404 she mentions the view formerly expressed as to the cause of the reversal of hair on the chest of man. This, also, I have reconsidered fully in Chapter XIII. where the action of the platysma muscle is held to be the cause of that remarkable reversal.

On page403 the mistake I made in calling the reversed area over the ischial tuberosity of the ischium in a dog a whorl is pointed out. This is corrected in Chapter VI. on the Dogs.

These three are the only errors of any importance that I acknowledge at once. A certain number of minor points are questioned in the Review, and the theoretical portion is strongly criticised. It would be irrelevant to the main purpose of a book which is limited to the subject of Habit and Hair Direction in Animals to introduce some of the more debateable branches of the subject of the former book, such as tufts, the direction of the hair on the mole, the classifica­tion of the hair-streams of the mammalian body into primitive, those modified by morphological change, and those due to use and habit. This last is a very wide subject and is far beyond the present limits.

I freely make another acknowledgment. The whole of the subject of the Direction of Hair in Animals and Man was taken up ad hoc, that is to say, for the purpose of testing the unpopular doctrine of Lamarckism. If this be an offence against the highest spirit of science, I can but accept the charge with a sigh, and go on, “faint yet pursuing.” There is consola­tion in finding that increased study of a subject is bringing order out of chaos, even if the field be small and the immediate crop poor.

The following are some of the objections raised to the theoretical part of the book:—

The most serious charge against my interpreta­tion of the mode of formation of patterns (whorls and tufts) is that there is a lack of harmony between my preliminary statement that whorls are due to motor or muscular causes and a subsequent explana­tion of some of them as due to external pressure. I did not state then as clearly as I do now in many passages in the present chapters that for pattern produc­tion there may be at least four causes: friction, pressure, gravity, underlying muscular traction, and that whorls and featherings may, of course, arise from some other external force acting on the hair at the decisive point of struggle, just as well as from the more common cause—muscular traction on the skin. I think in this region of the Review and where she deals with Selection, she shows signs of that scientific monism which is still affecting many of our great biologists, that is to say, they desire a world-empire in evolution for the great factor of Selection, and will stretch their arguments considerably to save its face. This is shown in the Review on page406 where a very thin plea is put in on behalf of adapta­tion and Selection in regard to hair-directions, as in man’s minute hairs, which cannot be seriously maintained. That earth is stopped!

Darwin’s open-minded dualism in this matter of the factors of evolution appeals to me at any rate more than the jealous attitude of Weismann and his eminent adherents.

Miss Whipple is less determined than I am in claiming for Selection the cause of the primitive slope of hair in mammals. It is the only conceivable arrangement that could exist for the advantage of the primitive forms in their simple life, and is, I submit, as much a matter of adapta­tion to needs governed by Selection as the possession of a dermal covering itself.

One more point, which, I think, is a small one and a fair one to raise, is worthy of a few remarks. Miss Whipple states that before variations in hair-direction can be logically attributed to external forces (giving the instance of the human scalp) “it should be shown that a change in the direction of the external, more or less wiry portion of the hair produces a change in the direction of the follicle.” As it happens, this change is easily seen in the case of the reversed hairs of the human forearm, if the hair be dark and the skin thin. The essence of the theory that dragging on the skin by muscular traction causes the hair to change its direction is that the relatively important portion within the hair-pit is pulled here or there according to the incidence of the prevailing force. But it is, to my mind, very clear that much repeated friction or pressure or gravity acting on the external and longer portion of the hair must, in course of time, drag the portion buried in the skin with it and so change its direction. These two portions of a hair cannot be arbitrarily separated. Shortly, one may say that the push of a force is as evident as the pull. A similar change in the direction of the buried part of a tree-trunk from a prevailing wind can be traced.

The last point is that I “omit to explain the mechanical process by which divergent muscular action could affect hair-direction.” This is well answered in the chapter on “Can muscular action in the individual change the direction of the hair?” for there it is shown by numerous examples in the human eyebrow that the muscles underneath the hairs which are embedded in the true skin for a tangible depth, do play havoc with the normal arrangement of hair, as the conflict proceeds, the resultant “pull” being actually engraved, signed and sealed by physiological wrinkles of the forehead and face.