 Dear students, in this topic we shall discuss the viscosity of blood and its effect on flow. Plasma relative viscosity is about 1.8, i.e. plasma is about 1.8 times viscous than water. Blood viscosity of plasma increases when blood cells are added, so the viscosity of whole blood in mammals and birds is about 3 to 4, i.e., blood is thicker or viscous than water 3 to 4 times. Dear students, according to Poiseville's law, the flow of blood in blood vessels is inversely proportional to its viscosity. Larger pressures are required to maintain the flow of viscous blood through the blood vessels. Dear students, the flowing blood in arterioles behaves as if its relative viscosity is much reduced. The apparent relative viscosity of blood approaches to the level of dataplasma i.e. about 1.8 only in vessels which are less than 0.3 mm in diameter. This is because of a phenomenon called plasma skimming. In the process of plasma skimming, red blood cells accumulate in the center of the vessel and the peripheries are relatively free of cell area generated. This type of viscosity between the center and the periphery becomes different. This is called plasma skimming and it increases the velocity of blood flow in blood vessels. Dear students, the phenomena of plasma skimming and the resultant increased flow velocity is known as parious linguist effect. This effect reduces the energy required to drive blood through micro-circulation. Parious linguist effect is inverted in capillaries i.e. the apparent viscosity of blood increases in capillaries. This is because the red blood cells move in a queue in capillaries and they press against the walls. This is because the blood flow increases in resistance and the blood velocity becomes slow.