Hygiene is the name given to that department of inquiry which deals with the causes and prevention of disease in their relation to the preservation of health. As thus defined, hygiene, while it is founded on medical experience, and while it is advanced by medical research, stands out clear and defined from the ordinary run of the science and art of medicine which deal with the cure of disease. The aim of hygiene is to prevent disease by the due appreciation of the causes which induce a departure from the normal type of healthy life. In this sense it has well been named Preventive Medicine, since it seeks to anticipate the work of the physician by its endeavour to remove the causes on which the diseases that affect mankind depend. Hygiene presents for consideration two chief phases. The first section of Personal Hygiene relates to the individual as a unit and to his duties in the maintenance of health, and in disease prevention. The second section deals with Public Health, and concerns the relations which exist between masses of men and the conditions of healthy living. In the first case the study embraces such subjects as food, clothing, habits, heredity, and the like, which relate to the personal history of the unit. In the latter case hygiene has to regard the community and the nation, and to investigate the laws under which disease is liable to be propagated by the circumstances of collective life. The departments of hygiene which deal with drainage, healthy houses, the removal of waste, and the prevention of infectious disease illustrate the subjects with which the public sanitarian or health officer concerns himself. It is of importance, however, to note that, as regards these two aspects of hygiene, their scope is by no means so restricted and so limited as the terms of their definition might seem to imply. For public health, as may readily be shown, can only be advanced by the endeavours of individuals. It is the individual and personal culture of health which not only must precede, but which also forms the foundation of public sanitation.
The history of hygiene forms in itself a study of much interest, and teaches us that, like most other branches of modern science, that of health has exhibited a gradual evolution and a cumulative advance. Very far back in the history of mankind we may trace the presence of the ruling idea of hygiene, that disease could be prevented by attention to the laws and conditions of healthy living. That the hygienic codes of the Jews were remarkably full and complete is evident from a perusal of the Mosaic books of the Scriptures. These laws, dealing with questions of food and feeding, with the isolation of the sick, and with the removal from camps and dwelling-places of waste matters, were of singularly enlightened character. The modern Jews have profited by the attention paid by their forefathers to questions of sanitation in the shape of their greater relative longevity, and their freedom from the scourges and plagues that have decimated the nations amidst which they dwell. The great desire of the ancient Jew that his days might be long in the land, and that his race should grow strong and multiply exceedingly, bore a very evident relation to the practice of those health laws according to which immunity from disease is secured and longevity encouraged. So that early enough in the phases of human development and civilisation sanitary science began to be studied in view of its obvious effects upon both personal and national welfare. The Greeks may also be quoted as a nation given to make a special study of the conditions of healthy living; but in their case the culture of a high standard of physique probably included most, if not all, the points to which this ancient people paid attention. They entertained a lofty ideal of physical beauty, and attained this ideal undoubtedly through the practice of much that partook of the character of hygienic science. Apart from this bodily culture, however, the Greek was not a sanitarian in the true sense of the term. He was visited by epidemics and plagues, which were regarded as signs of displeasure on the part of his deities. He made no attempt to discover the causes of these scourges or to arrest their course. Sanitation in Greece of old was therefore more a thing of chance than of scientific nature; and of ancient Rome the same opinion may be expressed. Great public works, and most notably those connected with water-supply and drainage, were certainly undertaken and carried out on a scale of magnificence; and so far these measures must have aided in the maintenance of the public health; but plagues were frequent and loss of life excessive as in ancient Greece, and of the laws of health as we to-day understand that term the classic nations seem to have been nearly ignorant. Medicine itself was of course in its infancy; and for this reason—viz. the lack of knowledge of the causes of disease—the health of the ancients was largely a matter of chance.
The record of progress in health science naturally follows the course and track of ordinary history, and in this respect forms a most interesting comment on the social advance of the people. The middle ages with ourselves, for example, beheld personal health neglected and public health unknown. Cleanliness was conspicuous by its absence; the 'sanctity of dirt' was respected by priest and people alike; the houses were built closely together; their domestic appliances were of the rudest description; and drainage was non-existent. The conditions of ordinary existence were those of rapine and war, and under such circumstances it is not wonderful that the science which devotes itself to saving life should scarcely have made its influence felt at all. The clearest proofs of the utter neglect of sanitation were to be found in the fevers and plagues with the records of whose frightful mortality the story of the middle ages teems. Dr Guy, who made a special study of the history of the epidemics of the middle ages, tells us that in the 12th century no fewer than fifteen epidemics and many famines were recorded. The 13th century saw twenty plagues and nineteen famines; while the 14th beheld in its early part eight epidemics and a succession of famines. In 1348 came to England the Black Death or Great Pestilence. As the result of this plague, which attacked Europe from the East, 100,000 persons died in London alone. In Europe at large it was estimated some 25 millions of persons died from this plague. The Sweating Sickness attacked England in 1485. This was a plague which was apparently propagated within the bounds of our own land by the filthy and impure surroundings of the people. After being attacked by the sweating sickness, the victim usually died within twenty-four hours. It attacked the well-to-do and intemperate livers especially, and appears to have been more fatal in the case of men than of women. After a succession of reappearances this epidemic passed away in 1551, and has since that date been extinct. A century or so later (in 1666) came the Great Fire of London, a catastrophe which was not an unmixed evil, since it cleared away the Old London with its foul and close houses, and induced the erection of a new and more sanitarially built city. The great fire apparently gave the coup de grâce to the Great Plague, which prior to 1666 had swept from time to time across the country, but disappeared in that year, happily to return no more. The cessation of the epidemic plagues thus enumerated was doubtless due to the abolition or modification of the conditions under which they had previously flourished. Less crowding together of people and of their dwellings, a freer atmosphere, and a greater measure of cleanliness doubtless acted then as now in abolishing epidemics; but even in the 18th century smallpox, typhus or jail fever, scurvy, ague, and other diseases continued to be only too well represented as legacies of the ignorant and careless living which characterised the preceding era.
It is, however, in the 18th century that hygiene begins to appear on the social horizon with something of clear outline and defined aims, as a distinct branch of science, pursuing a very practical relation to the lives of men. The Black Death and other plagues had then disappeared as we have noted, and thus the chances of prolonged life had become materially increased in Britain and in other European countries as well. The sanitary historian of the 18th century has to take account of at least three great names as those of fore-runners in the work of hygienic progress. John Howard (q.v.), the philanthropist, largely based his work of jail reform on improvement in the terrible state of these places of detention. They were overcrowded, and filthy in the highest degree, and, as a consequence of these conditions, typhus fever (which is a disease of overcrowding) reigned rampant under the name of 'jail fever.' Howard by his undaunted efforts succeeded in clearing the jails of this pest; and to-day our criminals reap the fruit of Howard's philanthropy in the fact that the jail now ranks in reality as the healthiest of dwelling-places. It is no exaggeration to say that if our homes could be rendered sanitary to the same extent as are the jails of our land, the death-rate would be speedily reduced to a minimum compared with its present amount. Captain Cook, the navigator, stands out as the second of the sanitary pioneers of last century. He it was who first showed that scurvy, which is essentially a blood disorder, and from which whole ships' crews used to remain prostrate in long voyages, was due to improper feeding. In one of his voyages Anson lost 600 out of 900 men from scurvy. Cook in a three years' voyage lost only four hands out of 118, and not one of these four deaths was due to the seaman's pest. He showed that in the absence of fresh vegetables, lime-juice should be served out regularly to ships' crews (see SCURVY). To-day Captain Cook's discovery is duly acted upon in the case of long voyages; and the extinction of scurvy in this fashion may be regarded as parallel in importance to the prevention of ague through the draining of the swamps and morasses amid the decaying vegetation of which the ague germs breed and multiply.
The third discovery of importance in sanitation in the 18th century introduces us to a feature in disease prevention which demands especial notice, because of the renewed importance which the prin- eiple in question has acquired in our own days. This feature may be called that of the modification of disease. It began, doubtless, far back in the history of eastern nations, if we are to credit Hindu records, but in 1720 Lady Mary Wortley Montagu, wife of the English ambassador to Turkey, introduced it to the notice of English physicians under the name of inoculation. This practice came into vogue as a preventive of smallpox in its pristine severity. Here smallpox matter, taken from the pustules of a person suffering from that ailment, was inoculated into the bodies of healthy persons. The result as a rule was that they acquired a mild attack of the disease, and this attack was found to prevent a future invasion of smallpox. Inoculation undoubtedly did not limit the spread of smallpox—indeed, as can be seen, it favoured its spread—but it undoubtedly tended to modify that loathsome ailment, and to prevent the dreaded scars and deformities which resulted from the disease in its full vigour. Later on came Jenner's discovery of vaccination. This practice began about 1796. Here matter taken from the pustules of cow-pox was used to 'vaccinate' the human being, the result being that a mild attack of cow-pox (or allied disorder) was given to children, and this was found, and still is found, in the vast majority of cases to be preventive of smallpox. The subject of vaccination need not be discussed here; reference may be made to the article on that subject; suffice it to say that since 1840, when vaccination began to be made the subject of legal enactment in Britain, and since 1853, when free vaccination was provided for the poor by law, smallpox has decreased both as regards frequency and severity. In 1867 vaccination was made compulsory for infants, and at the present time, even if it has not effected a universal escape from smallpox attack, we may congratulate ourselves upon a tremendous saving of life from this disease by its aid.
The advance of medical science—and especially the progress which has been made in microscopic research into the causes of disease—together with the spread of education, and of a consequent intelligent interest in health science among the people, has tended powerfully to awaken national endeavour in matters both of personal and public hygiene. In Britain the law has stepped in, and has provided, by means of many suitable enactments (1848, 1875, &c.), full encouragement in the pursuit of healthy life, as well as protection against health dangers. Each town or district is provided with its medical officer of health, and with its sanitary inspectors, whose duties comprehend the abolition of nuisances and the general supervision of drainage and other sanitary details. To-day it may be said that we possess a very fairly equipped staff of health experts in every large town, able and eager to assist and advise the citizens in the discharge of their manifest duties to themselves and their neighbours in the observance of hygienic rules. One of the most important enactments, for instance, is represented by the law which in many towns makes compulsory the notification to the authorities of every case of contagious disease which falls under the notice of the householder or medical attendant or both. In this way it is sought to limit the spread of those infectious ailments which add so largely to the death-rate each year. The authorities, being early informed of the appearance of any cases of these diseases, can take prompt measures for their isolation and their removal, if need be, to hospital. One case of smallpox, of typhus fever, or of scarlet fever may readily become, by neglect, the parent of thousands of cases, with a probable mortality frightful to contemplate; whereas by prompt isolation of the first case or cases misery, pain, loss of money, and chances of death may be saved to thousands. The seaports, too, are now narrowly watched by the health officers of these ports, and suspicious cases of illness on vessels arriving in harbour are at once dealt with. Cholera, it may be mentioned, which has run unchecked on the continent of Europe on several occasions within late years, has thus been warded off from the British coasts by the active supervision of the health authorities at the ports.
Within the sphere of the home health science has made of late years satisfactory progress. The principle of safe and sanitary drainage, whereby a house can be trapped off efficiently from the public sewers, and the inroads of sewer-gas (giving rise to typhoid fever and other ailments) prevented, is beginning to be everywhere practised. Plumbers are now encouraged to undergo examinations, instituted first of all by the Plumbers' Company of London, and to acquire thereby certificates of registration showing their knowledge of the principles on which house-drainage should be constructed. The vile 'scamping' work in the matter of drains so prevalent in former years, and so fraught with danger to the inmates of houses, it is to be hoped will be effectually banished from our midst. Here, as elsewhere, in sanitary science, the intelligent interest shown by the public in hygiene is beginning to bear fruit. The householder is no longer content to leave the sanitary arrangements of his house in the hands of ignorant architects or equally ignorant plumbers. His interest in his health affairs and his demand for sound sanitary work is a species of demand for which the inevitable supply is forthcoming in the shape of the increased attention now being paid to the construction of closets, baths, drains, lavatories, &c., and to the efficient protection of the house from the inroads of drain effluvia. In other details also the health of our homes is receiving the care it deserves. Questions of ventilation and of lighting are being studied anew, and the warming of houses is no longer left to chance. Personal health, which ranges in its extent from questions of foods and drinks to those of cleanliness and clothes, is not neglected amid the general improvement in hygienic education; so that the outlook in health questions is on the whole of the most hopeful kind. Happily the people at large are beginning at length to perceive and to act on the great truth that only by their personal education in hygiene, and by their knowledge and observance of health laws, can they secure the length of days which of old it was declared Wisdom bore in her right hand.
As a final point deserving of mention in relation to the acquirement of hygienic knowledge we may refer to the spread of knowledge regarding the exact causes of those infectious or zymotic diseases to which reference has already been made. These diseases include such ailments as smallpox, typhus fever, cholera, typhoid (or enteric) fever, measles, looping-cough, diphtheria, scarlet fever, and like disorders. That they are responsible for a very large amount of our annual mortality is a stable fact, and it is interesting to note how the better knowledge of their causation bids fair to enable us to cope successfully with their attack. It is now generally admitted that each of these diseases arises from a specific living particle or germ which, sown in the body, under favourable conditions, gives rise to the disease in question. Each germ is derived from a previous case of the disease, and each disease, under ordinary circumstances, breeds true—that is to say, if we sow smallpox we reap smallpox, and not measles or scarlet fever; and so with every other disease. What is known as the 'germ theory of disease' has thus come to assume a paramount place and power in modern hygiene. Already we have become acquainted with the specific germs of many disorders. We know, for example, the Bacillus tuberculosis, or germ to which tubercle is due—consumption or phthisis being merely a form of tubercle, as that disease affects the lungs. The germ of relapsing fever is also known, and that of the splenic fever of cattle and sheep has been very fully studied. The fight of mankind against these fevers and allied ailments is thus in reality a combat with the germs to which they owe their origin. All attempts to limit these disorders by disinfection or otherwise are directed towards the destruction of the germs which are given off from each case of a given disease, and which, if allowed to escape into air or water, infallibly spread the ailment broadcast. The knowledge of the exact origin of such diseases is therefore a powerful weapon in the hands of the sanitarian. In other ways than by germ-destruction it is sought to protect man and animals against disease attack. Pasteur and others, by modifying the germs of a disease (e.g. those of splenic fever) by submitting them to varied conditions of temperature, &c., and by artificially propagating them in appropriate solutions, have succeeded in producing germs of altered and weakened power. These latter, used to inoculate animals, produce a mild form of the disorder, which protects against subsequent attack (see HYDROPHOBIA). This is the latest practical development of the germ theory itself. How far it may be extended to protect man against his enemies in the shape of disease germs the future alone can tell. Meanwhile, it is interesting to reflect upon the fact that there is at least a possibility of the abolition of many of the ailments which now affect us by the combined work of attention to the ordinary laws of health and the promotion of a high standard of physical development, and, it may be also, by the work of science in fortifying us by inoculation against the invasion of our disease enemies.
It may be added that the cause and advance of sanitation in England has been encouraged and assisted by various Health Exhibitions held in London and elsewhere, in which the latest sanitary inventions and appliances were shown. One of the fruits of the London Health Exhibition of 1884 was the publication of an admirable series of hand-books, written by eminent sanitarians and physicians, and dealing with the various phases of public and personal health. As regards the advance of sanitary science abroad, Germany has long evinced a thorough appreciation of the advantages of scientific instruction in hygiene, and the Sanitary Institute at Berlin, presided over by Dr Robert Koch, is in its way a model of what such an establishment should be. Laboratories for the study of public health science have been established in connection with most of the English universities; while the Royal College of Physicians of Edinburgh and the Royal College of Surgeons of London have built laboratories specially intended for the study of germ life, and for bacteriological investigations in relation to the production of diseases at large.
In the United States the supervision of health matters is delegated to Boards of Health, of which one exists in each state. These boards receive reports from medical officers and other experts, and publish each an annual report containing much suggestive matter for the guidance of health reformers and for the improvement of the public health at large. Quarantine, conducted on rational principles, with the rigid exclusion of diseases liable to be imported by immigrants, is made a notable feature of the sanitation of the United States.
See the articles BACTERIA, BATHS, COOKING, DIET, GERM THEORY, GYMNASTICS, HEALTH-RESORTS, Hos-
PITALS, HYDROPATHY, NURSING, MEDICINE, SEWAGE, VENTILATION, WATER-SUPPLY; also Parkes's Hygiene (1883); Galton's Healthy Dwellings (1880); G. Wilson's Manual of Hygiene (1886); Corfield's Health (1880); the present writer's Manual of Health Science (1885); Simon's English Sanitary Institutions (1890); Sir B. W. Richardson's Diseases of Modern Life, The Common Health, and his life of Chadwick; and books on hygiene by Stephenson and Murphy (1892-93), Willoughby (1893), and Lehmann (1893).