Communicable diseases are those which are cause by minute micro-organisms or bacteria which can conveyed from a diseased to a healthy person. From early, these diseases were known either as infectiously when they were transmitted through the air or contagious when spread from person to person by direct contact.
But these terms do not always describe condition accurately, as many diseases are conveyed by insects. For this rests the term infectious is commonly used for all such diseases, but the term communicable diseases is more accurate and is now frequently used.
In microscopic quantities, the bacteria are entered in to the body. The blood-serum being a very rich nutritive fluid and the body temperature is just favorable for their rapid growth. But immediately the symptoms of disease do not appear. Unless and until, the introduced bacteria are sufficiently multiplied they do not produce any reaction.
The time between the infection and the appearance of first symptom is known as the Incubation period- It varies in different diseases and depends on the severity of infection and the state of health of the person infected some infectious diseases confer permanent immunity to the patient while others give temporary.
The common communicable diseases as Measles, Diphtheria, Small Pox, Mumps, Whooping cough and Influenza are most readily transmitted in the earliest days of their onset.
Hence a teacher can save health and perhaps even life by careful observation, whether children appear in their normal state or exhibit any signs of serious illness. In this manner the teacher can not only preserve the health of the children, but also saves time and increases school attend.
They all pass from one person to another; each disease has a definite duration; each disease has a definite incubation period; except in the case of Diphtheria and Influenza, one attack is rarely followed by a subsequent attack of the same disease in the same individual.