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O

Opticrom
A brand name for the drug, Sodium Cromoglycate.

Osteoporosis
Loss of bone tissue resulting in bones that are brittle and liable to fracture.

Oxygen
An odourless gas that makes up one fifth of the atmosphere and is essential to most forms of life.

Oxyhaemoglobin
Bright red substance formed when the pigment haemoglobin in red blood cells combines with oxygen.