The Integrative Action of the Nervous System

me." Any predominance this proprio-ceptor in the leading segments may exhibit in the proprio-ceptive system is not there- fore in virtue of the quality of reaction at a distance. If pre-^? eminently important to the organism as a whole its pre-eminence^^ of importance rests on other grounds than does the importance of the great distance-receptors, — the olfactory, the visual, and the auditory. A posture of the animal as a whole — a total posture — is as much a complex built up of postures of portions of the animal — segmental postures (Bonnier) — as is the total movement of the animal — its locomotion — compounded of segmental move- ments. With the hinder part of its spinal cord alone intact the frog maintains a posture in its hind limbs. These limbs are kept flexed at hip, knee, and ankle. When displaced from that pos- ture they return to it. But if the animal be rolled over on its back it makes no attempt to right itself The decerebrate frog with its labyrinths intact and their arcs still in connection with the skeletal musculature maintains the well-known attitude before mentioned. If inverted it at once reverts to that. The laby- rinth keeps the world right-side up for the organism by keeping the organism right-side up to its external world. The cranial receptors control the animal's total posture as do receptors of the hinder musculature the segmental posture of the hind limbs when but the hind end of the spinal cord remains.

Thus the labyrinthine proprio-ceptors are largely the equi- librators of the head, and since the retinal patches are movably attached (in mobile eyeballs) to the head, and since each retina has its normals of direction conforming with those of the head, these equilibrators of the head are closely connected by nervous arcs with the musculature maintaining the postures of the eye- balls. The posture of the head in many animals is dependent on the musculature not of the head segments themselves but of a long series of segments behind the head. In many forms the motor organs that steadily maintain or passingly modify the position of the head in regard to the external world — con- veniently indexed by the line of direction of gravitation — are contributed by the skeletal musculature of many post-cranial

gments. Hence the labyrinthine receptor is in touch with all the segments of the body, and these in a measure may be regarded as appended to the otic segment. Destruction of the labyrinth in the fish, the frog, the pigeon, the dog produces not only malposture of the eyeball and the head, but of the limbs and body as a whole. The " knock-out blow," where the lower jaw conveys concussion to the otocyst, reduces in a moment a vigorous athlete to an unstrung bulk of flesh whose weight

»one determines its attitude, if indeed a reactionless mass can ; described as possessing attitude at all. The labyrinthine receptors and their arcs give the animal its definite attitude to the external world. The muscular receptors give to the segment — e, g. hind limb — a definite attitude less in reference to the external world than in reference to other segments, e.g. the rest of the animal. Our own sensations from the labyrinth refer to some extent, as said above, to this environment, that is, have some projected quality ; our muscular sensations refer to the body itself, e. g. contribute to perceptions of the relative flexions or extensions of our limbs. The arcs of the proprio-receptor of the leading segments control vast fields of the skeletal musculature, and deal with it as a whole, while ^■|ie arcs of the proprio-ceptors of the other segments work with ^%nly limited regions of the musculature. Hence, in conformity with this the proprio-ceptor of the leading segments possesses long internuncial paths, for instance, bulbo-spinal from Deiter's nucleus proceeding to all levels of the spinal cord.

We traced the reactions of proprio-ceptors of the limb to bear habitually a secondary relation to the reactions of the extero-ceptors of the limb. Similar secondary relation is evi- dent also between the reactions of the proprio-ceptor of the leading segments (the labyrinth) and the reactions of the extero-ceptors of those segments. These latter extero-ceptors were seen to be distance-receptors, and the reactions of distance receptors were seen to be signalized by their anticipatory char- acter. From secondary association with these distance-receptors the reactions of the labyrinth come in their turn to have antici- patory character. They retain, however, their own special

features of equilibration and tonus. The locomotion of an animal impelled by its eye toward its prey involves co-operation of the labyrinth with the retina. And the tonic labyrinthine reflex which maintains an attitude may be just as truly an an- ticipatory reaction as any movement is. The steady flexed pos- ture of the frog directed toward a fly seen on the aquarium wall is a co-ordinate innervation securing preparedness for the seizure of the food. Its character is as truly anticipatory as is that of any movement. We might speak of the animal as " at rest," but it is the tense quietude of the hunter watching quarry rather than rest, such as supervenes in sleep and other conditions where active innervation is actually relaxed or reflex action is truly in abeyance.

Nervous integration of a segmental series. By longitudinal integration short series of adjoining segments become in respect to some one character combined together, so as to form in respect to that character practically a single organ. It is con- venient to speak of such reflex reactions, confined from start to finish to a single integrated set of segments, as " short reflexes " giving " local reactions." Thus the vertebrate appendages called limbs are plurisegmental, but the individual segments constitut- ing the limb form in respect of the limb a functional group of such solidarity that their reactions in the limb are at any one time unitary.

The reflexes that extend beyond the limit of such a group are on the other hand conveniently termed ** long reflexes!' And it is in the integration of long series, or of the whole series, of seg- ments one with another, that, apart from psychical phenomena, the nervous system seems to reach its acme of achievement. Here it is that we see eminently what Herbert Spencer has insisted on, namely, that integration keeps pace with difl'erentiation. In the segmental series the nervous concatenation of the segments repeats broadly the kind of association evidenced within each segment taken singly. Broadly taken, each seg- ment has on the one hand a piece of the extero-ceptive field, a piece of the proprio-ceptive field, and a piece of the intero- ceptive field, though this last is wanting in not a few segments.

On the other, it has fractions of the skeletal, of the vascular, and of the visceral effector organs. Each segment has muscu- lature and glands on its outer and visceral surfaces. Some segments have also secretors discharging into body spaces. Each of these sets of features of the segments has in the series of segments a nervous system of some functional homogeneity. With these plurisegmental systems as with their unisegmental pieces in the single segment the same harmonies of interconnec- tion are observable. Thus, the nervous arcs embouching into the skeletal musculature start chiefly in the extero-ceptive field in so far as concerns execution of passing movements, in the proprio-ceptive field in so far as concerns tonic postures; and so on, as sketched above. If the receptors of the extero-ceptive field are regarded from the point of view of the nature of the agency adequate for each of their species, representatives of each species are found in almost every segment. In this way the functional properties of the extero-ceptive field form not one but several multisegmental organs or systems of organs. In each segment exist receptors responsive to mechanical, chemical, and radiant agencies respectively. There is thus formed a tango- ceptive system to which practically every segment contributes, a thermo-ceptive system, a noci-ceptive system ; so also a musculo- ceptive system, and probably the receptors of the intero-ceptive surface similarly constitute a homogeneous system, prominent among their adequate agencies being those of chemical quality. These systems of receptive arcs present, though more or less compound, a solidarity of action in each system that gives each some rank as a physiological entity.

Restriction of segmental distribution a factor in integration. The impulse to nervous integration given by regional restriction of a peculiar species of organ to a single segment has especial force where that organ is of especial importance. This is the case with effector organs subserving important actions of con- summatory (v. s. p. 326, 329) type, e.^. a sexual appendage, or the mouth. Such organs as these are of restricted regional dis- tribution and subserve important reactions of consummatory type. With the mouth is associated differentiation of organs around

it. Many postures and movements of the organism are advanta- geous or disadvantageous to the animal's existence mainly inas- much as they improve or disimprove the position or attitude of the mouth in regard to objects in the external world. Much of the long series of movements and other reactions initiated and guided by ** distance-receptors " themselves is by-play on the way to a consummatory reaction which requires an appropriate placing and attitude of the mouth. That there is only one mouth and that of limited segmental extent involves co-ordination of the activities of many other segments with the oral. Integration of pluri-segmental activity is effected here, as in the other cases, mainly by the synaptic nervous system. The fact that the mouth is usually placed near the leading segments of the ante- rior pole is therefore a further factor in differentiating the seg- ments at that end from the after-coming train. Thus it comes about that in many cases the animal consists of two portions broadly different in character but complemental the one to the other, the head and the trunk.

It is noteworthy that the increase of susceptibility instanced by the distance receptors is in each case restricted to a special patch, quite limited in area. Given a synaptic nervous system, no single item of functional arrangement more enforces integra- tion of an individual from its segments than the restriction of a special kind of receptor to a single area or segment in the whole series. The motor apparatus of many segments has then to subserve a single segment, since that segment is provided with a receptor of a species not otherwise possessed by the individual at all. For integrative co-ordination of that kind the synaptic nervous system affords in the animal economy the only instru- ment. Only by the formation of common paths can due advan- tage be reaped from a specially refined recipient path (private path) of locally restricted situation.

Further, the condensed setting of a group of specialized receptors favors thpir simultaneous stimulation in groups to- gether. Stimuli even of small area then cover a number of receptive points in the receptive sheet. Thus, ocular images of various two-dimensional shape tend to be better differentiated the photo-receptors the more closely the individual photo- jceptors lie together. More data are thus gained as a basis for lifferential reaction. Further, the juxtaposition of groups of specially refined recep- ►rs in one set of segments, the leading or head segments, con- luces toward their simultaneous stimulation by several agencies lanating from one and the same environmental object. Thus, le property of brightness and the property of odor belonging an object of prey may then better excite in unison a reaction the distant reagent, or excite more potently than would either property alone. And movements of the reagent itself are then more apt to intensify simultaneously the reactions of its two kinds of receptors. The collocation of the disparate receptors in one region will favor that which psychologists in describing sensations term *' complication," a process which in reflex action has a counterpart in the conjunction of reflexes excited by recep- tors of separate species but of allied reaction. This alliance of reaction we have seen finds expression as mutual reinforcement in action upon a final common path. Thus a reaction is synthe- sized which deals with the environmental object not merely as a stimulus possessing one property but as a " thing " built up of properties. A reflex is attained which has its psychological analogue in a sense percept.

The cerebellum is the head ganglion of the proprio-ceptive system. If the basis taken for classification of receptors be a physiological one with, as its criterion, the type of reaction which the receptors induce, separate receptive systems may be traced running throughout the whole series of segments composing the total organism. We have seen that such separate receptive systems may be treated as functional unities, extending through the segmental series. In any such system there is evident a ten- dency for its central nervous mechanisms, that is to say, the com- ponents of the central nervous organ which specially accrue to the system in question, to be gathered chiefly where the most important contribution to its receptive paths enters the central nervous system. The receptive system in question has as it were its focus at that place. Thus receptive neurones which

can influence respiratory movement enter the central nervous organ at various segments, but the chief respiratory centre lies in the bulb where the receptive neurones from the lung itself make entrance and central connection, the vagal receptors being preponderantly regulative in that function. And we have seen that a proprio-ceptive organ (the labyrinth) in the head seg- ments seems preponderantly regulative in those functions which the proprio-ceptive system subserves. The central neural mech- anism belonging to the proprio-ceptive system is preponder- antly built up over the central connections of this proprio-ceptive organ (the labyrinth) belonging to the head. Thither converge internuncial paths stretching to this mechanism from the central endings of various proprio-ceptive neurones situate in all the segments of the body. There afferent contributions from the receptors of joints, muscles, ligaments, tendons, viscera, etc., combine with those from the muscular organs of the head and with those of the labyrinthine receptors themselves. A central nervous organ of high complexity results. Its size from animal species to animal species strikingly accords with the range and complexity of the habitual movements of the species ; in other words, with the range and complexity of the habitual taxis of the skeletal musculature. This central organ is the cerebellum.

The symptoms produced by its destruction or injury in whole or in part in many ways resemble, therefore, the disturbances pro- duced by injury of the labyrinth itself. It also influences tonus very much as do the simple proprio-ceptive arcs themselves. It is closely connected structurally and functionally with the so- called motor region of the cerebral hemisphere, just as the simpler proprio-ceptive arcs and reflexes are closely associated with the mechanisms of extero-ceptive reactions. Knowledge is not ripe as yet for an adequate definition of the function of the cerebellum. Many authorities have defined it as the centre for the maintenance of the mechanical equilibrium of the body. Others regard it as the organ for co-ordination of volitional movement. Spencer suggested that it was the organ of co-ordi- nation of bodily action in regard to space, the cerebrum he suggested being the organ of co-ordination of bodily action in

spect of time. Lewandowski considers it the central organ for e " muscular sense." Luciani, the universally acknowledged thority on the physiology of the cerebellum, describes it as e organ which by unconscious processes exerts a continual enforcing action on the activity of all other nerve-centres. It is instructive to note how all these separate pronounce- ents harmonize with the supposition that the organ is the chief co-ordinative centre or rather group of centres of the reflex system of proprio-ception. The cerebellum may indeed be described as the head-ganglion of the proprio-ceptive system, and the head ganglion here, as in other systems, is the main

Iranglion. The cerebrum is the ganglion of the '' distance-receptors." By he ** distance-receptors " are initiated and guided long series of eactions of the animal as a whole. Other receptive reactions ptegrate individual segments; the reactions of the distance- ieceptors integrate the whole series of segments. It is in the sphere of reactions of these " distance-receptors " that the most subtle and complex adjustments of the animal therefore arise. In their neural machinery not only short arcs but long arcs, in-

^ Giving extensive internuncial tracts, figure largely. Chains of eaction conducive to a final reaction relatively remote are more evident with them than with other arcs. If appeal to psychical evidence be ventured on it is to the field of operation of the arcs of these distance-receptors that higher feats of associative memory accrue, and, though the phrase is hardly permissible here except w^ith curtailed scope, conation becomes more intel- ligent. Finally, in harmony with the last inference, it is over these " distance-receptors " and in connection with their reflexes and arcs that the cerebrum itself is found. The cerebrum constitutes, so to say, the ganglion of the " distance-receptors." Langendorff"^ has pointed out that a blinded frog resembles in its reactions a frog with the cerebrum removed: the elasmo- branch without its olfactory lobes behaves as if it had lost its fore brain. Edinger traces the genesis of the cerebral cortex to a distance-receptor, namely the olfactory organ.

The integration of the animal associated with these " distance- receptors " of the leading segments can be briefly with partial justice expressed by saying that the rest of the animal, so far as its motor machinery goes, is but the servant of them. We might imagine the form of the individual and the disposition of the sense-organs as primitively very simple ; for instance, a spheroid with a digestive cavity and sense-organs distributed especially over the external surface. Such an imaginary form we should expect under evolution to become modified. If a motile organ- ism, its contractile mechanisms would obtain mechanical ad- vantage (leverage) by its elongation in certain directions. The lengthwise extension of the vertebrate body and of its lateral motor appendages, e. g. limbs, are in so far such as might be argued a priori. Under evolution in motile animals adaptations securing appropriate leverage for the contractile apparatus appear, and length along certain axes is always a consideration in them. In animals with segments ranged along a single axis, the animal for the greater part of its length comes to be one great motor organ, complex and able to execute movements in various ways, but still a unity. The pole at which the great " distance-receptors " (visual, olfactory, auditory) lie is that which, in the habitual locomotion of the animal under the action of the motor train attached, " leads." The animal therefore moves habitually into that part of environmental space which has been already explored by the distance-receptors of its own leading segments.

The head is in many ways the individual's greater part. It is the more so the higher the individual stands in the animal scale. It has the mouth, it takes in the food, including water and air, it has the main receptive organs providing data for the rapid and accurate adjustment of the animal to time and space. To it the trunk, an elongated motor organ with a share of the digestive surface, and the skin, is appended as an apparatus for locomotion and nutrition. The latter must of necessity lie at the command of the great receptor-organs of the head. The co-ordination of the activities of the trunk with the requirements of the head is a cardinal function of the synaptic nervous system. Conducting arcs must pass from the cephalic receptors to the

contractile masses of the body as a whole. The spinal cord contains these strands of conductors in vertebrates and is from this point of view a mere appendage of the brain. A salient feature of these conducting arcs is that the nerve-fibres from the cephalic receptors do not run, as might perhaps a priori have J^en thought natural, direct from their cephalic segment back- ^■ards to reach the common effector paths upon which they ^■nbouch. Instead of having that arrangement, these fibres, ^ftarting in the cephalic receptors, end in the gray matter of the Central nervous axis not far from their own segment. Thence the conducting arc is continued backward by another strand of fibres, and these reach (perhaps directly) the mouths of the final common paths in the gray matter of segments of the spinal cord. This is the arrangement exemplified by the pulmono- phrenic and other respiratory arcs, the depresso-splanchnic arcs, the olfacto-phrenic respiratory arcs, the arcs between the otic labyrinth and the muscles maintaining posture in the trunk, and practically that of the retino-molor arcs connecting the retina with the muscles of the neck. It gives at least one synap- sis more than the first alternative would do. And each synapse is an apparatus for co-ordination ; it introduces a ^' common path'' And it is in the exercise of the distance-receptors with their extensive range overlapping that of other receptors that the reflexes which relate to " objects " in the sense that they are reflexes synthesized from receptors of separate species become chiefly established. The ramifications of the central neurones attached to these receptors are so extensive and the reactions they excite are so far spreading in the organism that their asso- ciation with the reactions and central mechanisms of other recep- tors is especially frequent and wide.

The distance-receptors are the great inaugurators of reaction. The reduced initiation of action which ensues on ablation of the cerebrum seems explicable by that reason. The curtailment which ensues is indicative of damage which their removal inflicts on reactions generated by the distance-receptor organs. By a high spinal transection the splendid motor machinery of the vertebrate is practically as a whole and at one stroke severed from all the universe except its own microcosm and an environ- mental film some millimeters thick immediately next its body. The deeper depression of reaction into which the higher animal as contrasted with the lower sinks when made spinal signifies that in the higher types more than in the lower the great dis- tance-receptors actuate the motor organ and impel the actions of the individual. The deeper depression shows that as the individual ascends the scale of being the more reactive does it become as an individual to the circumambient universe outside itself. It is significant that spinal shock hardly at all affects the nervous reactions of the intero-ceptors (visceral system) ; and that it does not affect the intero-ceptive arcs appreciably more in the monkey than in the frog. Its brunt falls, as we have seen before, on the reactions of the skeletal musculature. Not that in the highest animal forms the "distance-receptor" merely per se has necessarily reached more perfection or more competence than in the lower. In lower types, as in fish, are found " distance-receptors " of high perfection, but their ablation does not in lower types cripple in the same way as in higher types. It is that in the higher types there is based upon the " distance- receptors " a relatively enormous neural superstructure possess- ing million-sided connections with multitudinous other nervous arcs and representing untold potentialities for redistribution of so-to-say stored stimuli by associative recall. The development and elaboration of this internal nervous mechanism attached to the organs of distance-reception has, so far as we can judge, far outstripped progressive elaboration of the peripheral receptive organs themselves. Adaptation and improvement would seem to have been more precious assets in the former than in the latter.

And, as related to the former rather than to the latter, must be regarded the parallelism of the ocular axes and the overlapping of the uniocular fields of photo-reception which in mammals has gradually reached its acme in the monkey and in man. This overlapping yields, in virtue one would think of some process akin to Herbart's " complication," an important additional datum for visual space. This, together with promo- tion of the fore limb from a simple locomotor prop to a delicate

explorer of space in manifold directions, together also with the organization of mimetic movement to express thoughts by sounds, lave with the developments of central nervous function which ley connote and promote been probably the chief factors in lan's outstripping other competitors in progress toward that lim which seems the universal goal of animal behavior, namely dominate more completely the environment. Remembering lese conditions, it need not surprise us that the distance-recep- >rs more and more exert preponderant directive influence over le whole nervous system. To say this is to say no more than lat the motile and consolidated individual is driven, guided, id controlled by, above all organs, its cerebrum. The inte- grating power of the nervous system has in fact in the higher inimal, more than in the lower, constructed from a mere collec- ^on of organs and segments a functional unity, an individual of lore perfected solidarity. We see that the distance-receptors integrate the individual not merely because of the wide ramifi- lation of their arcs to the effector organs through the lower :entres ; they integrate especially because of their great con- lections in the high cerebral centres. Briefly expressed, their special potency is because they integrate the animal through its )rain. The cerebrum itself may be indeed regarded as the ganglion of the distance-receptors.

Argument : Nervous integration in relation to bodily movement and to sensation compared. Sensual fusion in a relatively simple instance of binocular vision. The rotating binocular lantern. Flicker sen- sations generated at " corresponding retinal points " ; absence of evidence of their summation or interference either with synchronous or asynchronous flicker of similar frequency. Their interference when the flicker is of dissimilar frequency. Talbot's law not ap- plicable to " corresponding points." Fechner's paradox. Preva- lence of contours under Weber's law and under binocular summation compared. The physiological initial stages of the reaction generated in either of a pair of corresponding retinal points proceeds without touching the apparatus of the twin point. Only after the sensations initiated from the right and left " points " have been elaborated so far as to be well amenable to introspection does interference between the reactions of the two (right and left) eye-systems occur. The con- vergence of nerve-paths from the right and left retinae respectively toward one cerebral region is significant of union for co-ordination of motor reaction rather than for synthesis of sensation. Resem- blances between motor and sensual reactions. The cerebrum pre- eminently the organ of and for the adaptation of reactions.

The animal whose nervous construction we have been attempt- ing to follow thus far, we have supposed merely a puppet moved by the external world in which it is immersed ; and we have sup- posed it a puppet without passions, memory, feelings, sensations, let alone ideas concrete or abstract. From time to time we have purposely invoked appeal to sensations and feelings such as our own experience of ourselves provides in order to see better whither lead the blind reactions of the thing that we have been imagining a fatal mechanism. Whether such sensations or feelings accompany or do not accompany the reactions we have been studying we have left open. We have tacitly consented that our point of study of those reactions leaves that question, to which the present time gives no clear answer, as one with which we are not concerned. But we may agree that if such sensations and

H feelings or anything at all closely like them do accompany the H reactions we have studied, the neural machinery to whose working H they are adjunct lies not confined in the nervous arcs we have so H far traced but in fields of nervous apparatus that, though connected ^B with those arcs, lie beyond them, in the cerebral hemispheres. ^B In the attempt to trace the integrative work of the nervous »^ system on its motor side, one of our leading principles has been ^ that of the " correlation of reflexes about a final common path!' I^p Owing to the convergence of many various reflex-arcs toward and their confluence in a common eff*erent path co-ordination in

I their use of that path obtains and is demonstrable. It has been shown that some reflexes are so correlated in regard to a final common path that their actions on it coalesce and rein- force each other. These are allied reflexes and have allied arcs. Good examples of allied reflexes and arcs are those which arise in receptors of one species distributed in one regional locality and subserving one and the same type-reflex ; such are the arcs from the shoulder region of the dog subserving the scratch-reflex. We have also seen that reflexes which use the same " final common path " but use it to difl*erent or opposed effect are so correlated in regard to it that one reflex can temporarily inhibit the other from use of the path. These reflexes we termed in regard to each other antagonistic. From these motor reactions it is natural to attempt to cross the gulf from movement to sensation. In the bulbo-spinal dog we may produce a flexion of the fore limb by stigmatic stimula- tion of the outer digit. A reflex in its motor expression to all outward appearance like the preceding we may also provoke by simultaneous stimulation of the skin of the innermost together with that of the outermost digit. Or we may evoke a similar reflex in the limb by stimulating simultaneously with the fore foot the opposite hind foot. Here there is no conflict between the reactions to the component stimuli. We may add further the simultaneous stimulation of the same side pinna. The reflex is then of more compound origin, but its component reflexes are so correlated about their ^^ final common paths'' to the fore limb that their actions there coalesce and reinforce. Further, we may

add to these stimuli others applied to receptors of species actu- ally different from any of the cutaneous and thus still further add to the sources of the total reflex ; and we may choose sources which are harmonious and the impulses from them flow together and combine. On the other hand, instead of adding factors that tend to combine in the production of a particular reflex we may excite simultaneously with other sources a source whose reaction is incompatible with theirs. Then struggle and rivalry ensue and the result may be inhibition of that particular reflex movement and appearance of some other.