1. Preventive medicine and hygiene

The beginning of hygiene can be traced back to antiquity. Preventive medicine began with the first primitive idea of contagion. Even in the time when epidemics were explained as due to the wrath of the gods, it was observed that certain illnesses apparently spread from person to person.

Gradually, the idea of contagiousness was associated with a number of diseases. Fracastorius, in his book De Contagione, published in 1554, proposed a classification of diseases into those which were contagious and those which were not. That some diseases were contagious was fairly obvious, but some apparently arose spontaneously without a traceable source.

The confusion was finally resolved in the latter part of the 19^th century by the work of Pasteur, Koch, and their followers. The causative relationship of specific microorganisms and infectious diseases was established and the part played by carriers, common water and food supplies, and animal reservoirs, in disease transmission was gradually elucidated.

With these advances in knowledge came the vision of the possibilities of preventing disease by community measures. Health departments were organized for the purpose of controlling the spread of communicable diseases by isolation and quarantine, sanitation, immunization and diagnostic services.

2. Pasteurization

Food spoilage is usually the result of microbial activity, and the wholesomeness of food depends largely upon the kind and number of microorganisms it contains. The quality of food is frequently inferior due to the presence of excessive numbers of bacteria. This is especially true of milk and dairy products.

The term pasteurization takes its name from Louis Pasteur who first employed moderate heating as a method to control the contaminating wild yeast and bacteria responsible for the spoilage of wine. He found that temperatures within the range of 50-60⁰ C, maintained for a few minutes, gave excellent results.

Nowadays we recognize pasteurization as a process of checking or delaying bacterial decomposition of food and other substances by exposing them to heat in such a manner as to effect a partial destruction of the contained microorganisms leaving alive only those that are in the spore stage.

3. Water and its relation to disease

Water is a vehicle for certain infections such as cholera, typhoid fever, dysentery and other diseases whose primary seat is in the digestive tract. It may carry inorganic poisons such as lead, or substances such as nitrate. It may be responsible for certain nutritional and dietetic disorders, and occasionally for conveying animal parasites, amoebas, worms, etc.

The greatest danger in water is pollution from human sources. All the discharges from the body (urine, feces, expectoration, secretions from the nose, and washings from the skin) find their way into our streams sooner or later, especially where modern water-carrying systems are installed for waste disposal. All sewage-polluted water must be regarded as dangerous. It is highly probable that the sewage of large communities contains typhoid bacilli and other causative agents in greater or lesser numbers, because even when no overt cases appear, carriers or missed cases may be expected.

4. WATER

Water is the greatest constituent of the body making up approximately two-thirds of the total mass of a mammal. Furthermore, of the substances immediately essential for life, water stands second to oxygen. Without oxygen we can only survive for a matter of minutes; without water, for a period of hours or days, depending on the circumstances. Relatively small changes in body water can trigger profound changes in function.

That we are dealing here with efficient regulatory mechanisms is apparent from such simple observations as the constancy of body weight from day to day, the need to void soon after imbibing a large quantity of fluid, and the increase of water intake on hot summer days.

Water is supplied in the form of fluid taken as such, but a surprising proportion also enters the body as an integral part of the food. Fruits and vegetables, as a rule, contain over 90 per cent of water, and the so-called solid foods between 60 and 85 per cent. It is difficult indeed to find a constituent of the diet which contains less than 50 per cent of water.