The receivers for gathering information, the receptors, are what we commonly call the sense organs. Scientists distinguish six sense organs which they consider the prin­cipal ones: those concerned with vision, hearing, equilib­rium, taste, smell and skin sensibility.

As for the ‘non-principal’ senses, they are innumerable. The skin, for example, contains a great number of receptors. Some respond to a slight touch (these are responsible for the ’sense of touch’), others respond to a stronger impact and their stimulation is perceived as pain. A third type responds to cold, and a fourth is sensitive to warmth. These are but a few of the long list of skin receptors.

The internal organs also have many specific receptors. There are receptors to determine the quality of the food that enters the stomach, others to measure the blood pres­sure, and still others to test the amount of carbon dioxide dissolved in the blood. We are never even aware that they are functioning. The information being constantly sent to the brain from the internal organs does not penetrate our consciousness.

The brain has to sort all this out, glean from it the impor­tant information and separate it from what is minor or of no relevance. For the human brain can digest no more than 50 bits in a second.

In the morning, before it wakes up, the brain gets down to work. It has to tune in its receivers to ensure the un­failing supply of important messages. This is no easy matter, for human and animal organisms have numerous diverse receivers, each perceiving only a definite kind of encoded information.