The Winged Chariot of Time

The Human Rhythms

Biological clocks in man are subtle, but a number of undeniably clocklike rhythms are present. The pulse normally beats at 75 times a minute; the lungs fill with air at a regular tempo, even the brain thinks more clearly at certain times of the day.

Many of the body’s rhythms seem to be timed by the 24-hour clocks which predominate in nature. Man needs a regular — usually nightly — period of rest. And even when he sleeps, the electrical impulses from his brain have their own special rhythms (see picture).

Longer cycles are evident in man. What may be a multiple lunar cycle shows up in the 120-day average lifetime of red blood cells.

However they are timed, all the rhythms must work in concert. If the cycles get out of step — as they do when a factory worker shifts from a day to a night shift — the resulting strain can lead to irritability and lapses in judgment.

The sleep-wake cycle, controlled by the brain is the most familiar biological rhythm in man; it influences the timing of many of the body's other functions.

Body temperature, regulated by the hypothalamus, varies each day, regularly falling to its lowest point during normal sleep, between 1 a.m. and 7 a.m.

Oxygen increases during the normal peak hours of the body's activity — whether or not activity is present.

Heartbeats normally occur 75 times a minute, but the rate drops slightly to a low point between 10 p.m. and 7 a.m.

Adrenal gland secretion dips during the sleeping hours, but rises before waking to prepare the body for the day's activities.

Kidney excretion of such waste products as potassium and sodium reaches its peak during the middle of the day.

Reproduction is dependant on the periodic production of ova by the ovaries, in cycles of about 28 days. Pregnancy usually lasts 270 days from fertilization to birth.

Blood count has its own rhythms; The number of red and white corpuscles falls to a daily low in the morning hours of the day.

Cell division, occurring throughout the body, takes place most frequently during the late evening hours.