HungerAuthor(s): A. J. CarlsonSource: The Scientific Monthly, Vol. 33, No. 1 (Jul., 1931), pp. 77-79Published by: American Association for the Advancement of ScienceStable URL: http://www.jstor.org/stable/15079 .

Accessed: 01/05/2014 10:52

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact support@jstor.org.

.

American Association for the Advancement of Science is collaborating with JSTOR to digitize, preserve andextend access to The Scientific Monthly.

http://www.jstor.org

This content downloaded from 62.122.78.83 on Thu, 1 May 2014 10:52:04 AMAll use subject to JSTOR Terms and Conditions

SCIENCE SERVICE RADIO TALKS 77

rays from space may be the connecting link to tie together in a satisfactory theory the present indications of the sun and of the variable electric currents in our atmosphere and within our globe as the ultimate causes of the earth's magnetism and its variations. There- fore, laboratory experiments have been conducted for some years by the De- partment of Terrestrial Magnetism of the Carnegie Institution of Washington in the study of the structure of the

atom and its magnetic properties through the artificial production of high-voltage radiations. Another con- necting link may be in possible modifica- tions in the physical properties in the higher atmosphere from those in lower altitudes of which we know. Researches in this connection await development of rockets capable of reaching heights from 25 to 50 miles or even more. Re- cent tests indicate early realization of technique to accomplish this.

HUNGER By Dr. A. J. CARLSON

DEPARTMENT OF PHYSIOLOGY, UNIVERSITY OF CHICAGO

MODERN research on man and animals permits us to stats the following facts concerning the nature and control of hunger. Whether we use the word hunger in its widest or most limited sense, it describes one of the most com- mon and most important experiences of living organisms. Hunger pangs have been felt by every individual of the human race and have unquestionably determined many of the actions of their lives. Whether other animals besides human beings feel hunger pangs is still a matter of conjecture, but, if we em- ploy the word hunger in its quite legi- timate sense as the total of conditions determining the ingestion of food, we shall not exaggerate in saying that hunger is the most potent single in- fluence in life. At times the sex urge is more of a drive to activity, but the sex stimulus is dormant in childhood and fails with advance i-n years, while hunger is potent throughout life.

Despite the commonness of the hunger sensation( to return to the more limited definition of the word), our knowledge of its real nature is far from final. It is not even easy to describe our subjective experiernce of it. If we call it emptiness or hollowness, we are not really describing what we feel. In-

stead we are expressing our knowledge that our stomach is empty of food when we feel that uncomfortable sensation in our midregion. The hunger sensation can be correctly described as painful epigastric tension and pressure, but this, too, is unsatisfactory.

A charactertistic element in the hunger complex is its intermittency, its occurrence in sharply defined periods. This is true even though the stomach is continuously empty and the physical activity of the individual is uninter- rupted. It seems to hold also for other mammals and for birds. In the lower animals, to judge by the motion of the empty stomach, it is nearly continuous.

Although in normal persons the hunger sensation must become excep- tionally strong to be markedly painful, the epigastric sensation of varying de- grees of pain is the indispensable sub- jective element. Frequently, however, there is a feeling of general lassitude or weakness. Sometimes headache, nausea, nervous irritability, restlessness and even fainting may appear as a part of the hunger complex. Strictly speaking, a certain degree of nervous excitability is a necessary effect of hunger of even moderate intensity, but in normal per- sons with stable nervous organizations

This content downloaded from 62.122.78.83 on Thu, 1 May 2014 10:52:04 AMAll use subject to JSTOR Terms and Conditions

78 THE SCIENTIFIC MONTHLY

strong hunger is seldom accompanied by any of these obvious manifestations of nervousness. In some individuals, on the other hand, the accessory phe- nomena may be so marked as tG crowd out of consciousness the central factor of hunger, the gastric hunger pangs.

When we feel hungry, why do we eat? The obvious reply is that we know that eating will relieve us of the pangs. But ho-w did we learn? A new-born infant can not know what effect the in- gestion of food will have on the hunger sensation, because he has never had food in his stomach. What induces the new-born animal to take food? Is it a matter of inherited reflexes (instinct) ? The feeding reflexes are present at birth, and so are the defensive ones which reject unpalatable and injurious substances. We have seen that hunger increases excitability. Hunger then probably causes the infant to put more things into his mouth, to be either swallowed or rejected. Palatable ma- terials in the mouth and any materials in the stomach stop the hunger pangs, and the infant animal learns by the trial-and-error method that by eating discomfort is changed to comfort.

The exact cause of the hunger sensa- tion is still a matter of dispute, al- though, to my mind, the theory of peripheral origin has been conclusively proved but not completely worked out. The peripheral theory holds that the hunger sensation is inaugurated in sen- sory nerve endings, mainly in the upper part of the digestive tract (stomach, lower esophagus and small intestines). Some investigators hold that the origin of hunger is in a hypothetical hunger center of the brain, which is stimulated by food deficiencies in the blood or brain tissues. There is experimental evidence that hunger may, in fact, often does, begin even before the stomach is completely empty and long before there could be any food deficiency in the blood or tissue. It has further been

shown by experiment that hunger pangs coincide almost identically, both in time and intensity, with certain strong rhythmic contractions of the stomach, which begin as the stomach is empty- ing and continue in intermittent groups until inhibited by the ingestion of some material or by some abnormal condition, such as strong emotion or the action of drugs. These contractions have been termed hunger contractions. I regard as conclusive proof that hunger pangs are initiated by these contractions (through some sensory mechanism which has not yet been determined) the fact that an artificially stimulated hunger contrac- tion in an otherwise quiescent stomach will invariably give rise to a hunger pang.

The existence of intermittent hunger contractions, as well as the several other types of movements of the stomach, has been ascertained by sev- eral methods of objective observation on the stomachs of normal and abnormal man and animals. The stomach may be observed either directly through a fistula, by means of the x-ray and barium in the stomach, or with the aid of a balloon, which, when inflated in the stomach and connected by a rubber tube to a recording instrument, will yield a continuous record of its movements.

In the normal human being a single hunger contraction endures on an aver- age of 30 seconds. They come in periods of from 30 to 45 minutes, which are separated by periods of repose from 30 to 150 minutes long. The individual contractions in each period are sepa- rated by periods of quiescence at first but are practically continuous at the end. In infants the periods of quies- cence are shorter, gradually increasing to reach their maximum in senile old age. This is what we would expect, knowing that body metabolism (rate of food combustion) decreases gradually from youth to old age. The stomach muscles do not seem to share completely

This content downloaded from 62.122.78.83 on Thu, 1 May 2014 10:52:04 AMAll use subject to JSTOR Terms and Conditions

SCIENCE SERVICE RADIO TALKS 79

this decline, since starvation, even in old age, will give rise to strong con- tractions.

The stomach is supplied with various sensory and motor nerves from the cen- tral nervous system. The function of these nerves seems to be, in general, one of modification, similar to that of the nerves to the heart in the regulation of the heart rhythm. Even when all the central nerve connections are severed, the stomach exhibits typical hunger contractions. In sleep, hunger contrac- tions are more vigorous and regular than in the waking state. During sleep there is a general decrease in activity of the central nervous system, evidenced by decreased activity in all the other neuromuscular mechanisms, such as skeletal muscles, blood vessels and urinary bladder. One might expect to find the same condition in the empty stomach. The phenomena of increased activity indicates that the tonus mech- anism of the stomach occupies a unique place in the organism.

Emotional states of the higher nerve centers, such as anger, fear and joy, in- hibit hunger contractions. Intellectual states, such as attention, reading and reasoning, have no distinct effect on the course of the hunger period. Contrary to popular belief, the sight or smell of food does not intensify hunger contrac- tions; if there is any effect it is in the other direction. In this case the hunger pangs are probably reinforced through some central mechanism. The basis for the view that hunger "cravings" can be changed at will is probably to be found in the fact that mild hunger contractions do not enter consciousness if the attention of the individual is diverted in any way. The attention to hunger is usually aroused, consciously or unconsciously, about the time the

individual is accustomed to eat. There- fore, if he changes that time, he can to a certain extent change his experi- ence of hunger pangs.

One of the chemical factors in the blood that has been shown to influence gastric hunger contractions and the conscious hunger sensations is the sugar. When the blood sugar is mark- edly decreased hunger is increased, and vice versa. This is probably one of the reasons we can so quickly appease hunger with candies or sugar, as this type of food enters the blood quickly.

Hunger is increased in such diseases as diabetes. It is decreased in fevers and in most disorders of the digestive system. Hunger is not directly influ- enced or increased by tonics. Appetite seems to be merely the memory of past experience (sight, taste, smell) with food. Appetite is therefore a pleasant subjective process or sensation, while hunger is built into the very framework of the animal machine and is not es- sentially modified by the experiences of the individual, except as this induces strong emotional states.

The hunger pangs, due to the strong contractions of the empty stomach, con- tinue throughout fasting almost to death. The view that hunger disap- pears after a few days' fasting is an error. But disturbances in our con- scious life can overshadow our hunger feeling or even change it to nausea. Thus we see that the working of the hunger mechanism requires a normal stomach with its sensory nerves, and also a normal or nearly normal brain. In the normal person, the hunger felt, even in prolonged starvation, is uncom- fortable, but not actually or acutely painful. There is no heroism in "Hunger strikes. "

This content downloaded from 62.122.78.83 on Thu, 1 May 2014 10:52:04 AMAll use subject to JSTOR Terms and Conditions