398 E. MONTGOMERY: SPACE AND TOUCH, II. certain hand and a certain foot, and no other member of my body, that are thus localised. I now feel my thumb in some definite place in space: I know that it is my thumb by dint of the peculiar quality of the sensorial awakenings emanating from it. Has this qualitative peculiarity been operative in the recognition of the spatial disposition of the feeling? To decide this question, I move my thumb to quite another place. The qualitative peculiarity of the feeling remains unchanged; yet I clearly recognise that it occupies an entirely different position in space. Consequently the qualitative peculiarity of the feeling cannot possibly have contributed anything to the space-perception here involved. And if I recognise the position of any one point of a member without the help of qualitative signs, I certainly recognise as well the position of all its points without such help.

The feelings of motion or innervation which-synthetically combined with such qualitative tactile characteristics-are held by Prof. Wundt to constitute space, I have shown to take no part in our original realisation of spatial dimensions. Therefore both synthetical factors of Prof. Wundt's spaceconstruction are ineffective.

In studying the history of the space-problem, as far as the material for such study has been accessible to me at my distant home, I am highly gratified to find that at least one investigator, starting from the much more obscure and difficult phenomena of sight, has nevertheless arrived at an essentially similar conclusion to the one I have reached by the psychophysical interpretation of a distinct and simple tactile experience. Prof. Stumpf, in his very able and elaborate treatise Ueber den psychologischen Ursprung der Raumvorstellung, has demonstrated that extension together with colour form part-contents of one and the same sensorial experience, and that this experience is immediately given without the help of muscular motion; not associatively or synthetically constructed with the aid of such. He also shows that the third dimension, distance or depth, usually attributed to the influence of motor realisations, is immediately recognised as forming part of our original sensorial experience; in fact that every spatial recognition involves all three dimensions.

(To be concluded.)

V.-RESEARCH.

ON THE TEMPERATURE-SENSE.

By HENRY HERBERT DONALDSON,

Psychophysical Laboratory, Johns Hopkins University, Baltimore.

1. Historical.

IN the course of an investigation undertaken with Prof. G. Stanley Hall and under his direction, it was incidentally observed that the sensation of cold was felt only at definite spots on the skin.

The fact was noticed in this way: The sensations of motion as derived from the skin were being studied by means of a metal point which was slowly drawn over the surface. When the motion of this point, which was controlled by a suitable apparatus, was very slow, it often happened that it seemed to stand still for a time or even be lost, when suddenly a sharp sensation of cold, distinctly localised, would recall its presence and position.

This occurred so often that I find in my protocol for April 18th, 1884, the note: "Point always felt as cold". This fact arrested my attention, and in connexion with the other work I made several maps of these cold-spots on different parts of the body. When the experiments had reached this point, an important paper by Magnus Blix (1)' came into my hands.

This investigator started from the law of the specific energies of nerves, and took up the study of the dermal sensations to determine, if possible, how well-founded was the contradiction which they apparently offered to this law. He employed unipolar electrical stimulation, using a pin for his small electrode, and made use of an induction-current so weak that it did not generally cause pain. He thus produced at one spot on the skin a sensation of pain, at another pressure, at a third cold, and at a fourth heat. These spots were distinctly localised, and never superposed on one another. He gave special attention to the spots from which sensations of temperature were to be obtained. These he studied by means of a small metal tube drawn out to a conical point (Fig. III., below), and so arranged that a current of water could be kept flowing through it, thus enabling the observer to maintain the point at an approximately constant temperature. Using this instrument, he investigated various parts of the skin, and mapped out the heat-spots and cold-spots in several regions. Further, he applied the crucial test: a heat-spot and a cold-spot having been found, the warmed point was applied to both, then the cold. No sensation followed the application of the warmed

See "References to Literature" at the end.

point to the cold-spot, or the cold point to the heat-spot; thus showing the complete differentiation of these temperature-organs.

Where the epidermis is thicker, he found that the stimulus must be stronger to get the desired reaction. This suggests that the so-called spots may only be the more superficial portions of the nerve-bearing layer of the skin, which is in reality all sensitive. That this is not the case, is shown by the fact that the stimulus may be applied to a neutral spot for an unlimited time, without giving rise to a thermal sensation. The general bearing of these results on the current theories is kept in view throughout the paper. Blix, therefore, concluded that we have separate nerves for heat and cold, and that these have distinct terminations in the skin, which can be demonstrated.

Somewhat after the appearance of this paper by Blix, A. Goldscheider (2) published the results of a very important series of experiments. He had been for some time studying the specific energies of nerves, and in this connexion was led to investigate the sensations of temperature. For detecting the cold-spots he used either fine brushes dipped in ether or capillary tubes filled with the same. For locating both the heat-spots and the cold-spots he used small brass tubes brought to a conical point at one end and closed by a rubber-stopper at the other; these could be heated or cooled as was desired. To exactly mark the spots when found, he used a thermæsthesiograph, by means of which a brush wet with Indian ink could be brought down quite exactly on the spot which had been previously stimulated. I regret, however, that he has given no account of precisely how he travelled over the skin with this apparatus, and thus developed his maps. Thus working, he found that temperature-sensations were roused only at definite spots. His maps show them as very much more abundant than either Blix or I found them.

As a rule the cold-spots are most abundant where the skin is most sensitive to cold, but what Goldscheider calls first-class spots, i.e., those which react strongly on moderate stimulation, may often be quite few in number, where the spots of all grades are numerous. These spots are not alike on the symmetrical parts of the same individual, nor are they alike on the corresponding parts of diffe

1 At this point explanation becomes unavoidable. I first learned of Goldscheider's work on this subject, through Nature for January 15th, 1885, which contained an abstract of a report made to the Physiological Society of Berlin on December 12th, 1884, by Prof. Eulenberg. In this abstract, mention is made of the work of both Blix and Goldscheider, but no mention of the place of publication. This was first discovered on March 13th, 1885, and on the following day I was able to consult the paper at the office of the Surgeon-General at Washington. At another point I shall state how much of my investigation is strictly independent, and how much is imitation of the work of the above authors. The mention of these dates, however, appeared to me necessary to prevent any misapprehension of the relation in which the various investigations stand to one another.

rent individuals. What has been said for the cold-spots holds true also for the heat-spots. These latter are on the whole less abundant than the former, and tend somewhat to occupy the spaces. from which the former are absent. There are certain spots which are roused only by excessive temperatures. Goldscheider notes also that a spot often stimulated loses its sensibility, apparently becoming exhausted, for it does not react well until a more or less long period of rest has been allowed. When a heat-spot is overheated, it sometimes happens that a hyperæsthesia is produced, so that even pressure from a perfectly neutral body gives rise to a sensation of heat. He calls attention to the often observed fact that the tactile and thermal sensibilities in different parts of the body do not vary uniformly, and he points out that the discriminative sensibility when measured on two thermal spots is, as a rule, much finer than when measured in the ordinary way, and that this discrimination is finer the more intense the stimulus. In certain parts, as, for instance, those in which it is finest, discrimination for tactile-sensations surpasses that for temperature

sensations.

These sensations of temperature can be roused by mechanical and electrical stimulation as well as thermal. In both cases the cold-spots are more easily discriminated than the heat-spots.

By sending a strong electrical current through the arm and parts of the hand and thus stimulating certain nerve-trunks, Goldscheider is able to get peripheral sensations of temperature; here, too, the sensations of cold tend to predominate. He finds these spots insensitive to pain or contact. A needle may be plunged into them, or excessive temperatures applied without causing any feelings of discomfort.

Goldscheider also mentions the commonly observed persistence of sensations after the removal of the stimulus.

In sketching a general theory of temperature-sensations, Goldscheider brings a certain amount of evidence against the views of Hering (15). This latter investigator, relying mainly on the fact that water of the same temperature may feel cold or warm according as the hand is brought into it from a warmer or a colder vessel, concluded that, when the susceptibility of the thermal apparatus is decreased from one kind of stimulus, e.g., heat, it is increased for the other, e.g., cold, and vice versa. The experiment which Goldscheider records is this: If one hand be put into a vessel of water at 40° C. and kept there for ten seconds, and If then both this hand and the one which during the meantime has been at the room-temperature be put into cold water, the warmed hand will feel the cold less distinctly than the one which has been kept in the air of the room. In going from a cold vessel to a hot one, heat is in the same way less distinctly felt by the hand which has been immersed. If, now, the view of Hering were correct, that the exhaustion for one stimulus was correlated with an increased sensitiveness to the other, we should expect the

immersed hand to feel the change of temperature more acutely than the other; but this, we have seen, it does not do. Goldscheider therefore inclines to the older view of Weber.

Goldscheider's paper is further continued by an interesting discussion of the other sensations of the skin-pressure, pain and tickling; but with those we are not at present concerned.

In a communication to the Physiological Society at Berlin (Dec. 15th, 1884), Prof. Eulenberg (3) states that he has been able, in the main, to corroborate the results of Blix and Goldscheider, but did not succeed in getting temperature-sensations by mechanical stimulation. In Eulenberg's paper, chemical stimulation is spoken of as having given positive results in Goldscheider's hands. As no mention is made of chemical stimulation in any of the published papers of Goldscheider which I have seen, I am inclined to think this statement erroneous.

The most recent paper is a note by Goldscheider (4) in which he reaches the conclusion that the temperature-nerves often radiate from centres, and that these centres often coincide with the hair-follicles.

2. Experimental.

As the work which had been in progress before the receipt of Blix's paper involved the use of metal points at the temperature of the room, it naturally followed that the cold-spots were alone noticed. The moment attention was directed to the heat-spots their existence was easily demonstrated.

My first endeavour was to make an accurate map of these spots on some portion of the skin. Maps had been made long before, but they had been quite rough, and hence it was deemed worth while to repeat the operation. For this purpose, the apparatus which had been previously in use was, with some slight modifications, employed. This machine was devised by Prof. Stanley Hall, and will be described in a forthcoming paper, under the name of the " Kinesimeter". The description about to be given is intended to make clear the use of this instrument in this investigation alone.

The essential part is a rectangular brass table T (Fig. I.), 36 × 33.5 cms. and 26.5 cms. high, supported on four legs. In the middle of this is a rectangular opening 25 x 5 cms.; over this runs the car R, the wheels of which fit into grooves on either side of the opening. It can thus be rolled from one end of the opening to the other. At the ends of the opening are seen the grooved wheels P' and P", about which passes the endless cord N N. This cord can be clamped to the side of the car, so that when the wheels are put in motion the car is moved. P" is geared with P so that the motion of P is transmitted to it; in this way, by putting my finger on P and slowly turning it, a slow motion can be given to the car.