Basic objective of this lecture is to present on Blood. By thus lecture you can able to understand the composition of Blood; realize the function of red blood cells and plasma. Here also explain the function of haemoglobin in the transport of oxygen and state the function of macrophages and lymphocytes. The average human has 5 litres of blood and it is a transporting fluid. Tt carries vital substances to all parts of the body. When there is a high concentration of oxygen e.g in the alveoli haemoglobin combines with oxygen to form oxyhaemoglobin.