Canadian Blood Services says the chronic shortage of blood donations is a long-term problem they face.

In the past two months, there has been a 40 percent drop in the blood supply and that has forced rationing. Through public pleas for help, there is now a four day supply of blood - up from a two day supply just two weeks ago.

At the permanent downtown clinic in Calgary, Jaff Van booked an appointment to donate his blood. "I heard the radio ad and felt obliged to come in," says Van.

Van gave blood once before - 10 years ago - but has already booked his next appointment for 56 days from now.

Canadian Blood Services says Van is the kind of donor they are looking for: young and committed. "We do have an aging population so the people there were once the committed donors are moving up in years and are now becoming the recipients," says Bonnie Monteith, a spokesperson for Canadian Blood Services.

The chronic shortage can also be explained by the increasing demand from hospitals. CBS says there is no one particular explanation but a higher incidence of trauma does play a role.

While the immediate crisis for an increase in blood supply is over, Canadian Blood Services says it now has to sustain its rate of collection in the long term.