particular quality in stated quantities at fixed intervals, and disturbances are bound to occur whenever the supply is diminished or adulterated. Elaborate ventilation devices must be installed in public buildings to insure an uninterrupted supply of good air; and the gaseous and solid impurities poured into the atmosphere of a great city cannot fail to affect the health and well-being of its inhabitants. Kelsey reports that the smoke emitted from Pittsburgh industrial plants contains about three million tons of sulphur yearly, or enough to dissolve 265,000 tons of iron, and that soot is deposited each year in central London at the rate of 426 tons per square mile.*

The organic needs of the human being are clearly many and various. Although they are obliquely dealt with in connection with the study of physiology, no investigator seems ever to have undertaken the difficult task of listing, describing, and classifying them all. That they are of the first importance in determining the primary satisfactions of life, and that no living arrangements can hope permanently to defy them, is beyond question. There is a constant pressure towards some degree of correspondence between these life needs and the activities of every group, though the adaptation is never very exact, and usually falls far short of what one might desire.

How social arrangements affect organic needs.

The pressure towards some degree of correspondence between organic needs and group activities does not work in but one direction. It is easy to show that group behaviors have the effect of defining precisely what these needs shall be. Among the basic human needs, for example, men rightly include the need for exercise and rest. Unless the muscles are frequently brought into vigorous play, the blood sent coursing through the veins, and the general level of bodily tonus heightened, we become flabby and soft in all our parts. Unless, on the other hand, we are able periodically to loll about and invite our souls while the body builds up what has been torn down under even the normal strains of life, we become restless and enervated. The character of this need for exercise and rest, however, has not remained unchanged throughout the course of human history. Who ever heard of a primitive man exercising for the sake of the exercise itself? Yet this is precisely what city dwellers of today are finding it necessary to do. The need for exercise has become crucial in their lives. Graham Wallas has pointed out how the conditions of modern life have called out of man, not only new forms of

fatigue and new susceptibilities to it, but also new capacities for work and effort.5

This same matter of work and play illustrates the curious inversions and adaptations among our activities that may occur without fatally transgressing biological law. Activities may become tied up with the satisfaction of needs which at first glance hardly seem pertinent to them. Work is usually regarded as the expending of strength or thought for the attainment of some outside end; whereas play is taken to mean activity engaged in for its own sake. Americans, however, are often accused of turning their play into work. Instead of pleasurably luxuriating in the loose and rather random release of energies when they play their games, the desire for mastery and success (both of which are, of course, external to the actual activities involved) pushes them on to the most strenuous exertions. Through laborious practice and great hardships they become exceedingly proficient, but only at the cost of turning their games into businesses requiring unremitting application. In order to husband their energies such persons are forced to treat their "work" as play.

Some rather remarkable features of American college life are here in point. Many students really do all their work on the athletic fields or in other extra-curricular activities, and merely play their way through their studies. The former activities have become the accredited channels of intense endeavor, and the classroom turns out to be a place for day-dreaming, idle speculation, mild surmise, and general intellectual looseness. The situation is not an entirely happy one, since the games really seem better adapted than the classroom to the purposes of play. Whether the classroom, however, is really adapted to the purposes of work is quite another question.

It is desirable to distinguish organic needs with pronounced social components from those which remain relatively unchanged from one environment to another. This we may do by calling the former developed or derivative needs. Needs of both types should also be distinguished from things which are merely desired, since it is obvious that a thing may be desired (or wanted) although it is neither an organic nor a derivative need, as these terms have been defined above. Thus a little child may beg for more candy, although (as we say) "It isn't good for him." Whether all organic needs are good for us is a delicate question that can hardly be answered in the present state of our knowledge; but it is possible for a derived need to be biologically harmful-as for example the socially developed need for certain stimulants.

The nervous system.

A short description of the nervous system is necessary, on account of its importance in our story. The cells which compose it are called neurones. They are found in the brain, in the spinal cord, in certain ganglia or groups situated outside the spinal cord, and as fibriles or processes extending out to all parts of the body, where they are in connection either with sensory nerve endings or with muscle fibers or glands. Neurones are not intimately welded together anatomically, but are separated by synapses or gaps, which nervous stimulations must be strong enough to cross. The situation at the meeting point of two neurones is usually something like that when the branches of two trees intertwine and touch, or nearly touch. Taken collectively these neurones are the channels of all experience. If anything ever happens to the body without affecting them, we never get wind of it. We could be burnt to death without ever knowing it, were it not for the functioning of the nervous system; anesthetics are drugs with the power of decreasing the sensitivity of portions of the nervous system; sleep is a condition in which the sensitivity of the nervous system in some manner is lowered.

The nervous system has often been compared to a complicated telephone exchange. This analogy drives home one very important truth-that all communication within the body goes on through nervous pathways.* The brain and spinal cord play the part of the central exchange in the telephone system. The regular course of stimulation, then, is as follows: A set of physical changes in the environment acts upon a group of sensory nerve endings, and causes them to transmit impulses through the incoming or sensory nerve processes to the spinal cord, where one of two things may happen: (a) (with the simpler forms of reaction) impulses are generated in outgoing or motor nerve processes and transmitted to muscle fibers or to glands, which are thereby caused to function; (b) (with the more complicated forms of reaction) the impulses are carried by one or more central nerve processes up to the brain, where they generate other impulses in central nerve processes which travel down the spinal cord, are transmitted to outgoing nerve processes, and in turn cause the functioning of muscles or glands.

The whole cycle of incoming (sensory), central, and outgoing (motor) processes is called a reflex arc, and it always acts as a

* Two exceptions to this rule must be mentioned: (1) Certain of the glands release secretions directly into the blood stream, which eventually carries them to the organs they are capable of affecting; (2) parts lying next to each other undoubtedly affect each other by purely physical pressures.

unit. The reflex arc concept is absolutely fundamental to an understanding of the operation of the nervous system, for it states that the nervous system is never activated except through the joint cooperation of stimuli, sensory processes, central processes, and motor processes. A muscle, for example, is totally incapable of acting on its own initiative; it must be excited to action by impulses that reach it through the stimulation of one or more reflex arcs. Nor does thinking take place in any other manner; it all goes back to the stimulation of reflex arcs.

The following is a classified list: (1) of our sensory organs, i.e., of the doors of entrance for stimulations to reflex arcs; (2) of our motor organs, i.e., of the doors of exit for stimulations from reflex arcs: 6

(1) Organs of touch and pressure; of sensibility to cold and to
heat; of pain; of general chemical sensibility; of hearing,
vision, smell, and taste; organs of muscular, tendon, or joint
sensibility; sense of equilibrium; organs of hunger, of thirst,
and of nausea; organs giving rise to respiratory, to circu-
latory, to sexual, and to cavity distention sensations; organs
of visceral pain; organs of abdominal sensation connected
with strong emotions.

(2) Organs on skeletal muscles, on visceral muscles, on glands,
and on special visceral end-organs.

From this list it can be seen that we obviously have many more than the traditional five senses.

The situation is rendered more complex by virtue of the fact that important parts of the nervous system (collectively called the autonomic system) are to a considerable extent cut off from direct connection with the brain and spinal cord. The autonomic system controls the vital processes connected with breathing, circulation of the blood, and digestion, plays a large part in sex life, and seems to be influential in determining the general feeling tone of the body which goes so far in fixing our temperamental attitude towards life. In the main the autonomic system lies outside the central nervous system, as previously described, but the central portions of its reflex arcs are located in the spinal cord, so that it forms a partially but not completely independent unit. It is itself divided into three sections as follows:

Cranial section-accelerates digestion and salivation; retards the heart; contracts the pupil; controls bronchial tubes.

Sympathetic section-controls sweat glands and blood vessels including those of outer body surfaces; accelerates heart-beat; checks digestive and sexual processes; constricts blood vessels; dilates pupil.

Sacral section-accelerates the operations of the organs of excretion and sex.

In general, then, the sympathetic section of the autonomic system acts upon the same organs as the other two sections, but

in the opposite direction. It will be observed that the organs under the control of the autonomic nervous system are just those especially active in emotional excitement, and it may therefore be regarded as the body's chief feeling system. It must not be forgotten, however, that the effects of the movement of muscles are also felt, and that these strains contribute to the total excitement we call an emotion, although muscles, of course, are innervated by the central nervous system.

General characteristics of human behavior.

Let us now cast our eyes over the whole reach and extent of human behavior, and see if its chief features can be summarized in a few simple statements which shall be definite and yet not do violence to the facts. Inspection will reveal at least five points of major consequence.

(1) The human organism is ceaselessly active. The infant is a going concern from the very start. Even before birth some of his movements can be felt, and countless others go unnoticed. It would be difficult to exaggerate the amount of movement going on in a human being, even when he is at rest or asleep. Live muscle, for example, exhibits tonus; that is, it is continually receiving excitations from afferent or incoming nerves, and is aquiver at the rate of ten or twelve vibrations per second. There is also a certain amount of non-neural tonus. In addition to these minor shakings and tremblings, gross body movements of every sort are continually in evidence. Multitudinous in number and almost infinite in variety are the activities of the human organism.

To ask in general, then, why men act is simply to waste words. And to ask the question in a specific situation is usually to raise a moral problem. Man requires no motive to act-though he is often at pains not to lack one. It is a monstrous assumption, says Dewey,8

that man exists naturally in a state of rest so that he requires some external force to set him into action. . . . In every fundamental sense it is false that a man requires a motive to make him do something. The whole concept of motives is in truth extra-psychological. It is an outcome of an attempt of men to influence human action, first that of others, then of a man to influence his own behavior.

With the establishment of this truth, a whole series of false and misleading theories of motivation disappear, and the stage is set for a description of how men really do act, of the concrete modes of response exhibited by them. Inquiry turns from the causes of action to the manner of its organization in the course of experi

ence.