was tested as well as the mouth and nasal capsules, and the nerves mediating the reactions were determined. The chem- icals used were hydrochloric, nitric, and sulphuric acids for acid stimuli; sodium, ammonium, and lithium chlorides for saline stimuli; sodium hydroxide for alkaline; cane sugar, dextrose, saccharine, and its carbonates for sweet; and quinine hydrochloride, picric acid, ammonium and sodium picrates for bitter.® The solutions were applied by means of a pipette. They were ejected slowly with the tip of the pipette 2 mm. from the skin of the fish. Stimulation of the mouth or spiracles is followed (when the stimulus is effective) by one or more violent gulps accompanied by a quick ejection of water through the bronchial openings and more rapid respiration. When the nostrils were stimu- lated there followed a quick jerk of the head. Stimulation of the different fins likewise produced characteristic re- actions. Stimulation of the dorsal, lateral, and ventral surfaces results in a movement which is a part of the gen- eral swimming movement. In general it may be stated that all parts of the body are very sensitive to acids and alkalis in very dilute solutions, less sensitive to salt and bitter substances, and not sensitive at all to sugars. Certain parts of the bodily surface are more sensitive to salts and alkalis than is the mouth. The outer skin and the mouth are equally sensitive to acids, while the mouth is more sensitive to bitter substances. In regard to the nerves mediating the response to chemical stimuli it may be stated that when the cord is destroyed the caudal part of the body becomes insensitive. This shows that the lateral line organs do not participate in these reactions (since destruction of the cord does not affect them). When the cord is merely severed from the brain the response to chemical stimuli is more ® These were made up in distilled water on the basis of the gram- molecular solution. The inorganic acids were prepared as normal solutions, titrated against an alkali of known strength for accuracy. The other solutions were made up by weight, the concentration first used as a test depending partly on the solubility of the chemical used. The chlorides were prepared as 5n solutions, the sugar, 3n, sodium hydroxide as n, saccharine n/6, quinine hydrochloride n/10, picric and its salts n/15. These solutions were gradually diluted until the limit of reaction was reached.
418 '' COMMON CHEMICAL SENSE " marked than before. Sectioning of that part of the fifth nerve which supplies the nasal passages {ramus maxillaris trigemini) produces insensitivity to chemical stimuli in that region, thus showing that the olfactory nerves do not participate in the reactions. Sheldon finds evidence that the ' ' common chemical sense ' ' is likewise distinct from the tactual sense. This evidence may be summarized as follows: Parts of the body may be fatigued for tactual stimuli and remain sensitive to chemical stimuli, but when any region is fatigued for a given chemical stimulus it no longer or rarely is sensitive to tactual stimuli. It usually remains sensitive to other forms of chemical stimuli, however. When cocaine is applied response to tactile stimuli dis- appears before response to chemical. Among chemical stimuli, sensitivity to bitter disappears first. These results are supposed to furnish evidence that the cutaneous mech- anism is separate from that of the '' common chemical sense." Similar experiments have been carried out upon the catfish {Ameiurus) and upon Ammocoetes by Parker, with results which confirm those of Sheldon.
" Common chemical sense " in amphibia. — The com- mon leopard frog (Bana pipiens Sclireher) reacts to chemi- cals much as does the fish. Cole, who made the tests, pre- pared brainless frogs and dipped them to the ankle in a given solution. After a few seconds the leg would be withdrawn in case the stimulus was effective. A frog dipped into distilled water does not so withdraw the leg. Solutions of the chlorides of ammonium, potassium, sodium, and lithium were found to be effective stimuli. Since these same solutions produce gustatory reactions in man, the question arises here, as in the case of the fish, does the frog 's skin possess a general chemical sense comparable with the special sense of taste? Cole is inclined to answer this question in the affirmative, since he was able to show that frogs which had been cocainized until pain reactions were abolished still responded at least once to the chemical stimulus (a 3 m. solution of ammonium chloride).
Summary. — While it has been shown beyond question that both the fish and the frog (.spinal) are sensitive to SUMMARY 419 acids on bodily surfaces, the experiments of Sheldon and Cole do not conclusively militate against the view that these reactions are mediated by the pressure-cold-warm-pain terminals (and apparently there are such specificities even though the sensory endings are not highly differentiated. See work of Hofer, p. 428). Their results can possibly be harmonized with the view that these receptors do mediate the response to acids by supposing that any or all of such terminals may be " inadequately " stimulated by the solu- tions; that their threshold of sensitivity is markedly altered by the chemicals; and that when superficial terminals are destroyed or otherwise made insensitive (fatigued?) the deep-lying cutaneous structures together with the kin^es- thetic (muscle spindles or their homologs, etc.) begin to function. However, Herrick supposes that the " common chemical sense " is the primitive one from which the ol- factory and gustatory have been differentiated.'^ BIBLIOGRAPHY Audubon, J. J., Ornothological Bibliography, 1835, II, 33.
Baglioni, S., " Contributions experimentales a la physiologie du sens olfactif et du sens tactile des animaux marins {Octopus et quelques poissons ),"Arc/i. Ital. de Biol., 1909, LII, 225.
" Zur Kenntnis der Leistung einiger Sinnesorgane (Gesichtssinn, Tastsinn, und Geruchssinn ) und des Zentral- nervensystems der Cephalopden und Fische," Zeitsch. f. Biol., " Zur Physiologie des Geruchsinnes und des Tastsinnes der Seetiere," Zentralhlatt fiir Physiologie, XXII, 719. BatesojST, W., " The Sense Organs and Perceptions of Fishes, with Remarks on the Supply of Bait." Jour. Mar. Biol. Assoc, United Kingdom, N.S., 1890, I, 225. Beebe, C. W., "New World Vultures," Part II, Zool. Soc. Bull, Cole, L. J., " Reactions of Frogs to Chlorides of Ammonium, Potassium, Sodium, and Lithicum," Jour. Comp. Neu. and Psych., CoPELAND. M., " The Olfactory Reactions of the Puffer or Swell- fish, Spheroides maculatus " (Bloch and Schneider), Jour. Exp.
'' Parker differs from Herrick and Sheldon in holding that the olfactory sense presents the primitive form from which the others have been derived. He is led to this view chiefly by the similarity of the olfactory neurone to sensory cells found in invertebrates.
420 " COMMON CHEMICAL SENSE " Hekrick, C. J., "On the Morphological and Physiological Classifica tion of the Cutaneous Sense Organs of Fishes/' Amer. Nat.
" The Organ and Sense of Taste in Fishes," Bull U. 8. Fish Comm., 1902, XXII, 237; also Bull, of Scientific Lab of Denison Univ., 1903, XII, 39.
Johnson, H. M., " A Note on the Supposed Olfactory Hunting Re sponses of the Dog," Jour. Animal Beh., 1914, IV, 76.
Parker, G. H., " The Olfactory Reactions of the Common Killifish Fundulus heteroclitus (Linn.)," Jour. Exp. Zool, II, 1.
" Olfactory Reactions in Fishes," Jour. Exp, Zool.
" The Relation of Smell, Taste, and the Common Chemical Sense in Vertebrates," Jour. Acad. Nat. Sciences of "The Sense of Taste in Fishes," Science, N.S., 1908, XXVII, 453. Parker, G. H., and Sheldon, R. E., " The Sense of Smell in Fishes," Bull. Bureau Fisheries, 1912, XXXII, 35. Read, E. A., " A Contribution to the Knowledge of the Olfactory Apparatus in Dog, Cat, and Man," Amer, Jour, of Anatomy, Romanes, G, J., " Experiments on the Sense of Smell in Dogs," Rouse, J. E., " Respiration and Emotion in Pigeons," Jour. Comp, Sheldon, R. E., " The Reactions of the Dogfish to Chemical Stimuli," Jour. Comp. Neu. and Psych., XIX, 273.
" The Sense of Smell in Selachians," Jour. Exp. Zool., Strong, R. M,, " On the Olfactory Organs and the Sense of Smell in Birds," Jour. Morph., 1911, XXII, 619.
" On the Habits and Behavior of the Herring Gull," Larus argentatus pont, The AuJc, 1914, XXXI, 21 and 178.
Watson, J. B., Animal Education. Chicago, Univ. of Chicago Press, CHAPTER XIV CUTANEOUS, ORGANIC, AND KINESTHETIC SENSES I. Cutaneous. — Cutaneous sensitivity in mammals. — Hahn's experi- ments upon the bat. — The " sense of support " in mammals. — Yoakum's experiments upon the temperature sense in mam- mals.— Contact sensitivity in fish. — Contact and temperature sensitivity in amphibia. II. The organic system. HI. The kinaesthetic system.
I. Cutaneous Cutaneous sensitivity in mammals. — ^Many mammals are well supplied with highly developed tactual mechanisms, such as hairy coats, vibrissse, etc. No mammal seems to be lacking completely in hairs. The vibrissas seem to be highly specialized tactual organs which play a considerable role in the daily life of many animals. It has been supposed that such specialized tactile organs are to be found mainly upon nocturnal animals. This position, however, cannot seri- ously be maintained. Vincent has made a careful histo- logical study of the vibrissas of the rat. Fig. 67 shows the structure of such a hair. Its rich sensory innervation and large arterial supply are apparent.
In addition to the tactile hairs, mammals are well sup- plied with highly specialized sensory endings in the dermal and muscular tissues. Vincent's investigation of the func- tion of the vibrissas in the daily life of the rat, and espe- cially in learning problems, the solution of which is de- pendent upon the functioning of the vibrissge, is the only comprehensive study we have upon the contact sense of animals. She constructed a simple maze, the runways to which were without sidepieces (restraining walls). The runways (4" boards lying horizontally) were placed far enough apart to keep the animal from jumping from CUTANEOUS SENSE one to the other. The maze was then raised 2 feet from the floor. The normal animals behave characteristically in this maze. In moving off after being put on the runway they go at first along the very edge of the board Fig. 67. — Longitudinal Section of Follicle This follicle was drawn from a Cajal silver preparation, but some features of the nerves and arteries have been added from other prepa- rations. It shows: a, nerve from dermal plexus running down to form the nerve ring; &, conical body; c, sebaceous gland; d, artery- entering ring sinus; e, ring sinus; f, nerve ring; g, dermal sheath; h, ring\vulst; i, root sheath; /, cavernous sinus with trabeculse; k, main sensory nerve from below; I, large artery entering with nerve; m, papilla. ' (From S. B. Vincent, Jour. Gomp. 'Neurol., Vol.
with vibrissEe dragging. They curl their toes over the edge and run with noses against the floor. The animals moved slowly at first, so there were few falls. Shortly bursts of CONTACT SENSE IN THE RAT 423 speed occurred and then falls became numerous at the turns. Finally, as in the Hampton Court maze (p. 103), the animals became automatic. The three photographs from Vincent's monograph show respectively a normal animal, a blind rat without vibrissse, and a blind rat with vibriss^e. The in- fluence of the vibrissa can be thrown into relief by cutting them from one side. Strange to say when the vibrissae are absent on the right side the animals keep close to the left Fig. 68. — Normal Animal with Vibrissa on Maze Without Sides Note the position in the center of the track, the way the feet are placed, the lifted head and body.
side of the path, and vice versa. When running they pass to the edge, turn the remaining vibrissge down, and follow the edges closely. Vincent has shown further that white rats can form the habit of entering an alley with corrugated sides when two smooth alleys are offered at the same time. Tactile hairs are much utilized in the learning of this prob- lem. When robbed of them the animal makes use of the bare snout. When the snout is made insensitive by cutting the infra-orbital nerve it can no longer form such habits.
424 CUTANEOUS SENSE It is evident from this work that the vibrissae are functional structures and that they serve as (short) distance recep- tors. The so-called " stereotropism " which such animals exhibit is probably no more a case of stereotropism than is the action of a blind man in keeping near a wall or the edge of the sidewalk. Experiments of Nicolai, where the salivary reflex was used as the indicator, show apparently Fig. 69. — Blind Rat Without Vibrissa Note the flattened body and the use of the toes and nose on the edge of the maze.
that the dog is sensitive to mechanical stimuli and that the localization of such stimuli is accurate.
Hahn's experiments on bats. — For a long time it has been known that blind, anosmic, and deaf bats were able to avoid objects in their way and even to avoid silken threads stretched closely together. Hahn, in his more re- cent work, states that the older experiments are lacking in scientific accuracy since none of his bats, even with sense organs intact, was able to do what has been claimed by the earlier experimenters for maimed animals. To test the mechanism by means of which they avoid obstacles, Hahn CONTACT SENSE IN BATS made the following tests: Bats were liberated in an un- ceiled room 15' wide, 18' long, 9' from floor to eaves, 12' from apex to ceiling. Pieces of black annealed iron wire 1 mm. in diameter were suspended from the rafters. These were spaced so that there was one wire to each 11" of space. The animals were tested under four conditions: (1) With eyes covered with glue and lamp-black; (2) with external ears and tragi excised; (3) with external auditory meatus stopped with plaster of Paris; and (4) with hairs of Fig. 70. — Blind Rat with Vibrissa Note the use of toes and vibrissse on edge of maze.
body and membranes pasted down with vaseline. On Myotis lucifugus we get the following percentage of hits in the various controls: Normal It is evident that vision does not play a large part. It is stated by Hahn that the ^' perception ^^ of a stationary ob- ject is probably due to the condensation of the air between the flying bat and the solid object that it is approaching — Eyes Ex. ears and Meatus Hairs covered tragi removed stopped covered 426 CUTANEOUS SENSE the drum membrane functioning chiefly as a contact organ. He states also that the fine bodily hairs have a function in the avoidance of objects.
The " sense of support " in mammals. — In experiments upon rats, chicks, turtles, and many other vertebrates the influence of the contact sense is apparent in their be- havior when placed on the edge of table-tops, etc. In trying to get blind rats to jump from one platform to another, Richardson found that "up to a certain distance the rat was able to step across with little difficulty; and the con- tact of the snout or vibrissse with platform 11. seemed to be the essential stimulus in the majority of cases." "...This (blind) rat would not allow his forefeet to leave the platform unless his vibrissae reported contact with some object. When the platform was beyond the reach of his vibrissse, the experimenter touched their tips with a pencil, whereupon he put out his forefeet to step over. " Small finds the tendency to withdraw from the edge of the table strong in very young rats. The guinea pig seems to be lacking in such reflexes. Chicks and reptiles seemed to be influenced in such situations more by visual than by contact stimuli. (See p. 362 for Yerkes' experi- ment on tortoise.)
Yoakum's experiments upon the temperature sense in mammals. — ^Yoakum has tested the temperature sense of gray squirrels and white rats by forcing them to form the habit of entering the warmer of two boxes. The apparatus used is shown on p. 92. The warmer box (Standard) was kept at 40°±2°C., the other (Variable) at 15°±2°C. When the habit was perfected the temperature of the Variable was raised to 25°±2°C. The habit was again perfected. The temperature of the Variable was then changed to 30°±2°C. The experiment had to be inter- rupted at this point, but it was carried far enough to show that the difference limen had not been reached. A similar series of experiments was carried out upon white rats with the temperatures S = 40°±2° C. and V = 24°±2° C. The rats readily learned to enter the warmer of the two boxes under such conditions. The D.L. to temperature was not SENSITIVITY OF FISH TO CONTACTS 427 obtained. Both these animals will pile up cotton, straws, etc., to form a nest when the room temperature is lowered considerably. While stimuli other than temperature will call out this burrowing response, it probably is often called out by changes of temperature in the room. Yoakum de- scribes the behavior of the squirrel as follows: " The animal's method of covering itself is interesting. The squir- rel will draw the shavings, or cotton, up in a pile in one corner of the cage, and will then burrow into it. When finally hidden in the pile, all that is visible is a portion of the tail; if this is drawn aside the tip of the' nose and finally the entire head becomes visible. The little animal thus lies curled up in its nest with the tail as the final addition to its covering."
Nicolai states that when cold is applied to a particular spot on the skin of the dog a conditioned reflex is called forth. If the cold is applied to any other spot, the reflex again follows, showing that localization is not very exact. By the same method it has been shown that the dog is sen- sitive to warmth and that cold may be reacted to differ- ently from warmth.
Contact sensitivity in fish. — Of contact sensitivity in fish in the narrower sense (pressure-temperature-pain) we know very little. Running through the experiments of Bateson, Baglioni, Herrick, Parker, and Sheldon we find abundant proof of the sensitivity to contact — to solid objects and to cotton wool, etc., but the observations have been more or less incidental. Herrick has brought out the fact that fish, which at first always respond to cotton wool, will eventu- ally learn to inhibit response to this and to react only when stimulated with food objects. Baglioni finds in the trigger fish, Balistes capriscus, that the skin of the fins and of the upper anterior surface of the spine, stimulation of which causes erection of the spine, are quite sensitive to contacts. In the dog fish, Scyllium, the following regions are quite sensitive: the immediate neighborhood of the outer gill slits, stimulation of which causes respiratory reflexes; the neighborhood of the spiracles; the regions around the eyes, and the skin of the lids, stimulation of which produces closure of the lids. The external surface of the skin as a 428 CUTANEOUS SENSE 428 CUTANEOUS SENSE whole was found to be insensitive. Hofer, however, has shown experimentally that the fish has tactile spots and warm spots upon the skin of the head but not in the skin of other regions. Lyon has made experiments on the fish's ability to orient to currents in the water when in darkness. He had previously shown that the fish swims against the current (head up stream) through visual reflexes (p. 361). When tested in darkness the same reaction was observed, due to the contacts between the body of the fish and sta- tionary objects. In the light of Hofer's work on the func- tion of the lateral line organs it is probable that Lyon 's con- clusions will need confirmation.
Contact and temperature sensitivity in amphibia. — The contact and temperature sensitivity of the frog is some- what better known. It has even been stated (Steinach) that the frog possesses " touch spots " but the evidence is far from being conclusive. Babak has recently studied the temperature sense of the frog by a new and very sen- sitive method which promises to be very useful in behavior. He has found that the breathing rhythm of a frog with the fore-brain removed proceeds with machine-like regularity, interrupted only when the animal is stimulated and re- sumed shortl}^ after the stimulating agent is removed. In the maimed frog lung ventilation also occurs only after stimulation. In his first paper upon the sensitivity of the frog, the second of a series of studies upon the breathing rhythm, the author takes up the sensitivity of the animal to temperature as determined by changes in the breathing rate. The animals used had completely recovered from the shock resulting from operation upon the brain. The temperature stimuli were applied by means of the thermass- thesiometer held at a distance of 1 mm. from the animal's skin. The actual temperature changes in the skin could be judged only approximately. During experimentation great care was required to avoid auditory and tactile stimuli, etc. The specimens studied were found to be sen- sitive to slight changes in either direction from the physio- logical zero point. For comparison Babak obtained the threshold in human beings by applying the temperature THE ORGANIC SENSE 429 stimulus 1 mm. from the skin surface. The frogs, if the above reaction may be taken as an indicator, are fully as sensitive as man. The head region is most sensitive. It is possible by this method to work out a complete to- pography of dermal temperature sensitivity. The experi- ments of Yerkes on the auditory-tactual reactions of the frog have already been noted on p. 388.
II. The Organic System There seems to be no way at present whereby we can deal with organic responses in isolation. In one way organic stimuli and the responses to such are fundamental and basal — behavior to visual, auditory, and other sense stimuli is conditioned by the organic situation in which the animal finds itself. Physiology has claimed this province particu- larly. In recent years this science has shown itself amply competent to work out the many delicate problems which are inherent in this field. The work of Cannon and his students and of Carlson upon the nature of the muscu- lar contractions of the stomach in the absence of food; of Cannon on the effect of fear and rage on the secretion of glycosuria; and finally of Osborne and Mendel on the factors influencing growth are producing results which certainly bear as directly upon behavior problems as they do upon more strictly physiological problems. On p. 25 we touched upon the possibility of carrying out ex- perimental work upon the influence of the " sexual state " upon the general reactions of the animal. There seems to be no good reason why we should not study habit formation in animals robbed of the efferent nerve supply to these regions (and hence robbed of '' re- turn " or sensory impulses). Already there is a certain amount of work upon the structural changes which occur in a developing organism when ovariotomy is re- sorted to and upon ovarian transpkintations. The interest in such experiments, however, has been morphological. It is probable that the whole instinctive repertoire shifts in such cases and that the mechanism of habit formation is 430 KINESTHETIC SENSE profoundly modified. When we look for a moment at the behavior complexes present in migration, mating, hiberna- tion, etc., we can see that there must be rhythmical intra- organic factors which must be taken account of even by one who is primarily engaged in observing the behavior of animals to extra-organic stimuli. Jennings has well brought out the necessity of the study of such processes in investigating the behavior of lower organisms. The neces- sity of study in these fields is not less when we deal with the vertebrates. It is here primarily that the behaviorist and the physiologist meet. The behaviorist has not the equip- ment and the technique to engage in such studies and he must await the needed results at the hands of the physiol- ogist.
III. The Kinesthetic System If we made the statement that all of the work upon habit formation in all of the behavior laboratories (excepting the studies upon birds) points to the fact that the kingesthetic sense is the most important system of receptors, and yet that there was not one single thing that we could say about this sense in isolation, paradoxical as it might seem, it would not be far from the truth. When the author's ex- periments upon blind, anosmic, and deaf rats were made some twelve years ago, where it was shown that the daily lives of such animals were little affected by the loss of these distance receptors, it seemed to be a very special case. Since that time the view that the kingesthetic sense is the one most depended upon by animals where possible (i.e., that kingesthetic data are substituted for auditory, visual, and olfactory) has been confirmed by similar experiments upon many other forms. We need only to call attention to the fact that ' ' place ' ' or position habits develop rapidly in nearly all tests upon vision, audition, olfaction, etc. We have even found it necessary to handicap or penalize this sense by the introduction of punishment in order to give the distance sense stimuli a chance to influence the organ- ism. The kinsesthetic system is peculiar with respect to the FUNCTION OF KINJESTHETIC SENSE 431 fact that we must work with it by the method of exclusion. We can eliminate by several methods the influence of vision, audition, and the other senses, but in view of the fact that the muscle is both the effector and the receptor we cannot isolate the receptor features without eliminating the possi- bility of obtaining diversified response. For this reason we cannot now view the functions of the various parts of this complex system in isolation (i.e., determine the relative importance in habit formation of muscular receptors, ten- donous receptors, etc.). The tremendous importance of kinaesthesis in adjustment is not limited to the lower or- ganisms. There is a growing tendency to make it respon- sible for man's so-called reactions to objects which are not {at the moment of reaction extra-organically) present. We mean here merely to reiterate the view already several times expressed that there are no centrally aroused sensa- tions and that even in ' ' thought ' ' there is always a move- ment of a muscular mass somewhere, presumably usually in the laryngeal and related mechanisms.
BIBLIOGRAPHY BabaK, Edward, " Ueber die Temperaturempfindlichkeit der Am- phibien," Zeit. f. Sinnesphysiol., 1912, XLVII, 34.
Cannon, W. B., " Recent Studies of Bodily Effects of Fear, Rage, and Pain," Jour. Phil., Psych., mid Sci. Meth., 1914, XI, 162 (summary of several articles by Cannon and his students).
Carlson, A. J., " The Hunger Contractions of the Empty Stomach During Prolonged Starvation" (Man, Dog), Am. Jour. Physiol., Carlson, A. J., and Luckhardt, A. B., " The Condition of the CEsophagus During the Period of Gastric Hunger Contractions," Am. Jour. Physiol., 1914, XXXIII, 126. (Several other articles by Carlson and by Cannon and their students on the secretions and movements of the stomach tissue have appeared in recent numbers of the Am. Jour, of Physiol.)
Hahn, W. L., " Some Habits and Sensory Adaptations of the Cave- Inhabiting Bats," Biol. Bull, 1908, XV, 135 and 193.
HoFER, Bruno, " Studien iiber die Hautsinnesorgane der Fische," Berichte aus der Kgl. Bayerischen Biologischen VersuchsStation Jennings, H. S., Behavior of the Loiuer Organisms. New York, Columbia Univ. Press, 1906.
432 KINESTHETIC SENSE NicoLAi. ( For summary, see Yerkes and Morgulis, " The Method of Pawlow in Comparative Psychology," Psych. Bull., 1909, VI, EiCHARDSON, Florence, " A Study of Sensory Control in the Rat," Psych. Monographs, Ser. No. 48.
Small, W. S., " Notes on the Psychic Development of the Young Wliite Rat," Am. Jour. Psych., 1899, XI, 80.
Vincent, Stella B., " The Function of the Vibrissse in the Behavior of the White Rat," Beh(wior Monographs, Ser. No. 5.
" Tactile Vibrissae of the White Rat," Jour. Comp. Neu.
and Psych., 1913, XXIII.
Watson, John B., " Kinsesthetic Sensations," etc.. Psych. Mono- graphs, Ser. No. 33.
Yerkes, R. M., " Space Perception of Tortoises," Jour. Comp. Neu.
Yoakum, C. S., " Some Experiments upon the Behavior of Squirrels," Jour. Comp. Neu. and Psych., 1909, XIX, 541.
INDEX Ability, Learning, Comparative, Abnormalities, in growth of transplanted tissue, 150 Abridgment, of learning process, Acquired Characters, recent ex- periments on, 175 Activity, in sympathetic mechan- isms, 24 Adaptation, to background, 353 Adaptations, asserted forms of, Affection, as a form of instinc- tive behavior, 21; attributes of, 21; Stumpf-Woolley view Age, influence on learning of,