In Chapter 2, we described the health criteria set for blood donors and explained the need for high standards in donor selection in the interests of recipients because of the potentially lethal quality of human blood and the dangers of transmitting disease. We saw also that, in the interests of the donors’ health, strict limits had to be placed on these acts of giving. The young, the old, the sick and the disabled, expectant and nursing mothers, and other clinically ineligible groups are medically forbidden to donate; thus, something like one-half or more of the population are dependent in terms of their therapeutic and prophylactic needs for blood and blood derivatives on the remaining half or less of the population – healthy, able-bodied men and women. Some with blood of a rare group will depend for their lives on the willingness to donate of a very few unseen people with identical blood. Others, like haemophiliacs, may have to rely, year after year, on the gifts of fifty strangers every year for their continued survival (see Chapter 12).

For those who are eligible to give to the unknown few or the unknown many, there are also limits to giving both in relation to the quantity of blood that may be donated at any one moment in time and to the intervals of time between donations.

The doctor, informed by science, decides which biological groups in society should be allowed to take part in the act of anonymously giving blood and the endeavour to save life. He determines the circulation of givers.

The doctor also decides which individuals should receive blood – and blood of a particular group – though he does not know the giver; nor does he know whether the gift is a good one. In determining the circulation of gifts, he depends in large part on and has to presume the honesty and truthfulness of the giver. No society in the modern world has established laws and penalties to enforce the giving of blood and of truthful information by the giver concerning his state of health. But it is only in recent years that every country's need for blood on a large and rapidly increasing scale has raised in a new and impersonal guise these fundamental questions of social relations; of giving, receiving and repaying.