Blood is liquid connective tissue which connects all the parts of body and body cells acts as a principal circulatory medium of animals to bring about the humoral inter communications and transport of materials in the body.
With the entry of food into the alimentary canal, the salts and water are found absorbed in it. But other particles composing the food are so large that they cannot be absorbed directly. It is necessary to break down them to fine particles for diffusion. This process is called digestion and is brought about by enzymes.
Mammals are the highest group of vertebrates occupying the top position in the evolutionary history. They include approximately 5,000 living species and numerous fossil forms. Mammals have been evolved from cotylosauri on reptiles.
Complex food stuffs like carbohydrates, fat and protein need to be digested or hydrolysed before assimilation. The final product of carbohydrate digestion is monosacharides, that of fats are fatty acids and glycerol and of protein are amino acids.