All these chemical theories of exhaustion or of intoxication are certainly more important than those we previously considered. They are in accord with the observation pure and simple that fatigue generally induces sleep and that sleep is a recuperator. They render intelligible the alternating between wakefulness and sleep. They are also the best-known theories and the ones generally adopted. Claparède, however, who has examined these theories, objects to them as insufficient, and argues against them as follows: First, there is no parallelism between exhaustion and sleep; one can sleep without being tired; great fatigue may disturb sleep. Second, according to the chemical theories, the alternation of waking and sleeping might assume a type of periodicity with short phases. Claparède says:

Here is an individual who goes to sleep at midnight; at 10 minutes before midnight he was-M. de la Palice can not dispute it-still wide awake. Why was he not asleep at 10 minutes before midnight? Our physiologists say it was because the toxic waste products had not then become sufficiently concentrated. But then why does not this same individual awaken at 10 minutes or quarter past midnight since, if sleep stops the accumulation of the toxic wastes without restricting their elimination, their relative proportion in the system would then return to what it was at 10 minutes before midnight; that is, to a proportion favorable to awaking.

Third, the toxic theory of sleep is antiphysiological, for it is singular that a process of intoxication severe enough to necessitate eight hours of sleep should be repeated daily without at last causing serious disorders. Finally, all the facts that have come under our observation in regard to sleep-voluntary or involuntary drowsiness, voluntary wakefulness, and the like—are not explainable by a chemical theory, no more than are other multiple forms of sleep, than the physiological phenomena that accompany it, nor the dreams. An observation of Vaschide and Vurpas on the Siamese twins shows well the weakness of the chemical theories of sleep; in fact, these twins, whose blood vessels communicate, often sleep or wake one after the other and one could sleep while the other suffered from insomnia.

In a general way, all physiological theories of sleep fail to successfully explain it, for none of them can take account of the psychological phenomena which accompany it. We have seen that a person sleeps or stays awake voluntarily or from habit, a condition that is not within the province of the physiologist either to study or to explain.

Claparède, who has so well observed the impossibility of a physiological solution, alone has sought to explain it by a theory both psychological and physiological, which he has called the "biological" theory of sleep. This biological theory is most interesting and ingenious. It merits a place by itself and will hold our attention for a time. According to Claparède, sleep is not merely a passive, negative condition, a cessation of the organic functions. On the contrary, it is itself a function, a positive activity, having its own biological

significance. One goes to sleep before the moment of complete exhaustion and in order to prevent it. Sleep is a function for the defense of the organism, and we have the desire to sleep before feeling an overpowering need of it, just as we are hungry and thirsty before there is an imperative necessity for eating and drinking, just as the swallow migrates before it is overcome by the cold, as a bird builds its nest before the time for laying its eggs. All these instinctive acts, all these instincts, begin before there is an absolute necessity. This conception of sleep as an active instinct preceding exhaustion changes the question entirely. Sleep is no longer a categorical positive necessity, but it becomes a very pliable, modifiable act. Like all instincts, it is regulated by the law of momentary interest. We sleep if our interest in slumber is the greatest at a given moment; but we could ward off sleep if some other instinct should predominate. This pliability of instinct enables us to understand the variations of sleep, the various causes of drowsiness and awaking. It enables us to understand dreams. The theory of Claparède has therefore a great advantage over all the others, since it alone can be applied to all the varied forms of sleep. Further, it does not exclude physiological theories, since it can accept them as stimuli of the sleep instinct. Inhibition, the fatigue-producing substances, the sensations of fatigue, and the like, become the causes of the interest that we take, at a given moment, in going to sleep.

But Claparède's theory reaches beyond the sphere of pure physiology into that of psychology. Nevertheless, it offers a new field of activity for the physiologist, who, relieved from the anxiety of searching for a complete explanation for sleep, need no longer be deterred by the inadequacy of his own theories, but may seek to complete and state precisely those parts of the biological theory of Claparède that pertains to his own peculiar sphere as a physiologist and are not yet solved. Sleep is an instinct of defense, but defense against what? This instinct is brought into play by various stimuli, but which of these are physiological? We shall not inquire further as to why we sleep, nor as to what it is that makes us sleep, but ask what does sleep protect against? What is it that gives us a desire to sleep? My friend Piéron, lecturer at l'Ecole des Hautes-Études, has asked himself these questions, and has wished very much that I would help him to answer them. For six years we have been making numerous experiments to try to solve the problem, and it is the actual result of our researches that I would like to explain to you in concluding this lecture.

Sleep is an instinct that obeys a law of momentary interest, and there is very little hope of finding a physiological cause for its being brought into play. This explains why the physiological phenomena which accompany sleep are often not constant, why we can not

consider them as the causes of sleep, and, in fact, they appear very often to be the consequences rather than the causes.

But sleep is an instinct of defense, of protection. Against what does it protect? Will not the suppression of sleep, insomnia, show us the reason for that instinct, by exaggerating its causes; may we not the better see what belongs to the domain of physiology? We have been led to keep animals awake so as to study what happens to them under these conditions. The first difficulty was to prolong wakefulness with the least fatigue; in fact, the effects of fatigue might hide or disturb the very conditions that we may wish to study. Various experiments with severe and prolonged work, such as observations of deer driven at the course, have enabled us to distinguish the effects of fatigue from those of insomnia; and we have succeeded in preventing some dogs from sleeping while tiring them as little as possible.

Even under these conditions prolonged loss of sleep is always very serious, and after about 10 days the animals have generally reached the limit of resistance. During the entire period of this wakefulness the need of sleep becomes more and more imperative, and one can see among the seeming physiological factors of sleep those which tend to increase it and effect the need of sleep and those which do not disturb sleep and consequently can not be considered as its causes. The temperature of the body remains normal, the respiration undergoes no variation, and the amount of carbon dioxide in the blood does not increase, which enables us to exclude the theories of the impoverishment of the blood in oxygen and its enrichment in carbon dioxide as actual causes of sleep. Neither the blood nor the brain lose their portion of water, and this fact combats the theories that explain sleep by dehydration. Toward the tenth day the animal can no longer keep its eyes open; its paws are continually bending, it has lost all sensorial activity and only the strongest kind of stimulation will induce reaction. At this moment the brain shows cellular disturbance, localized exclusively in the frontal lobe, such as could not have been brought on by other means, and which, therefore, seem to be characteristic of insomnia. If such an animal is left to sleep at will, he plunges into a deep sleep from which he awakens completely refreshed, normal, and the alterations in the brain have then disappeared.

Prolonged wakefulness, therefore, is thus shown to bring on an imperative need of sleep and some cellular modifications in the frontal lobe of the brain. To what are these phenomena due? Is it to exhaustion or to intoxication? We are thus brought back to reexamine some of the chemical thoeries for which we sought to find an experimental basis.

If the need of sleep is due to an accumulation of toxic waste products in the organism, one ought to be able, by injecting these substances into a normal animal, to communicate the necessity for sleep. Our first experiments in that direction were unsuccessful. By injecting into a vein of a normal dog some blood or serum taken from a dog exhausted by loss of sleep, we had no very definite results, although in some cases we brought on some modifications of the cells of the frontal lobe, and by injecting these same substances directly into the brain we were no more successful. Could it, therefore, be concluded that wakefulness is not accompanied by the accumulation of toxic substances, and is caused only by the impoverishment of the nerve cells? This conclusion was possible, but it might equally be the case that the blood of the normal animal destroyed the substances injected in small doses, or that their quantity was too small. To remove this last doubt we made our injections by another method. There exists, in the interior and around the nerve centers, a liquid called the cerebro-spinal fluid, which completely envelops them. You can get this fluid either at the lower end of the spine, and is there reached by lumbar puncture, and in spinal anesthesia, or between the occipital bone and the first vertebra, at the level of the fourth ventricle of the brain, and it is there that we operated. To be sure, the operation is a delicate one, but it can be performed with a little practice. By observing certain necessary precautions, such as avoiding compression, one can without danger or trouble make injections at that level. The serum, or, better yet, the cerebro-spinal fluid, of an animal exhausted by loss of sleep, if injected under these conditions into a normal animal, produces in the latter in about half an hour an imperative need of sleep. The animal so injected is benumbed little by little, its eyelids blink, its limbs relax, its eyes close, it loses all attention, and it responds but feebly to strong stimulation. Its brain presents the characteristic lesions of insomnia. The injections, under the same conditions, of liquids from a normal animal have no effect at all. You, therefore, may conclude from these experiments that it is possible to transmit the absolute need of sleep from an exhausted animal to a normal one, and also that the liquids of exhausted animals have a property or contain a substance capable of producing sleep. If it is indeed a substance, do you ask me what it is? I can not yet tell you. It is that very research which is at the present moment occupying our attention.

This rapid review of the question of sleep will have shown you that it is a most complex problem. I would wish that it would likewise give you the impression that although physiology alone can not dream of solving the problem, it can at least offer a profitable contribution, and that its share, when it is contented with facts, is not less than the contributions of other sciences that are busy with the same problem.

PROFITABLE AND FRUITLESS LINES OF ENDEAVOR IN

PUBLIC HEALTH WORK.1

By EDWIN O. JORDAN,

Professor of Bacteriology, University of Chicago.

It is in accord with the spirit of this congress to consider public health questions either from the point of view of things already accomplished by the application of the scientific method or from that of things to be done. I have chosen to speak especially of "the saving of waste and increase of efficiency" still to be expected when public health problems are approached in a scientific spirit.

It is well recognized to-day by many experts that while some of the ordinary activities of municipal health departments are of unquestionable value in conserving the health of a community, others are relatively ineffective or possibly worthless. One well-known writer 2 has thus expressed himself on this point:

I boldly assert that if every case of communicable disease were promptly reported to the proper local board of health and as promptly placed under effective sanitary control and so kept until danger of infection had passed, all the other present-day activities of boards of health, whether local, State, or national, with the exception of those directed against certain causes of infant mortality and the possible further exception of some food and drug inspection, might be dropped with no appreciable effect upon the general health or mortality of any of our States or most of our cities.

In all fairness it must be admitted that a part of the energy of almost every municipal health department in this country is devoted to combating imaginary dangers or applied to tasks that have only a remote bearing on the public health.

This condition, as a rule, is not due to ignorance on the part of health officials, but to the pressure of public opinion. Such pressure is often exerted directly through legal ordinances passed by uninformed legislative bodies, but sometimes also through agitation by mistaken enthusiasts or through other channels of public opinion.

1 Paper presented before the Congress of Technology, Boston, Apr. 10, 1911, to commemorate the fiftieth anniversary of the granting of the charter to the Massachusetts Institute of Technology. Printed in Science, June 2, 1911. Reprinted by permission.

2 M. N. Baker, chairman committee on municipal health and sanitation, National Municipal League.