Nutrient digest or infusion agar plus 5-10 per cent blood (of horse usually), oxalated or defibrinated, added at 55 C. Employed nutritionally for the cultivation of fastidious microbes, but also as an indicator of haemolysis caused by colonial growth products. Chocolate agar is formed by heating set blood agar plates at 60° C for an hour. Used particularly for Haemophilus spp. Penicillin and streptomycin may be added to blood agar for the selective cultivation of yeasts and fungi.