To remove blood stains from a mattress, a sofa or a seat, clean the mattress or the sofa completely with a sponge dampened with a solution of lightly diluted ammonia.
Rub vigorously, especially on the blood stains.
When using ammonia, open your windows wide and avoid breathing in the fumes. If possible, wear respiratory protection.
Completely clean the mattress or seat to avoid all residual stains. Dry the mattress or sofa with a flannel and hair dryer on a low setting.
You can also apply to the blood stains a paste of water and powdered starch or flour. Let stand for a few hours and then brush.
Or remove the blood stain from the mattress with a cloth soaked in white vinegar. Remember to rinse and dry after removing the stain.