Le sang, mode d'emploi" series: blood types

Blood fascinates as much as it frightens. It's also the subject of many false beliefs and a juicy business. When should you have your blood tested? Are blood tests sold on the Internet reliable? How can I get good-quality blood? What's the value of all those supplements you find everywhere? Do I need to adapt my lifestyle to my blood type? Are diets based on blood types useful? What happens to my blood when I donate it? What can I expect when I donate blood?