Health is one of most important things in our life. We think that it is a real luck to have a strong health. Our way of life doesn't increase the physiological condition of our body. Alcohol, cigarettes, unhealthy food, stresses and other factors have a great influence on our health. The human's immune system is very uncertain thing because there is a countless quantity of different dangerous viruses and bacteria. From ancient times plague and other infectious diseases have been killing people without leaving them any chance to survive.