A reader writes:

Would donating blood be considered one of the Corporal Works of Mercy?  It seems to, but at the same time doesn't quite fit into one of the 7 listed works.  The reason I'm asking is that I feel spiritually guided to start donating my blood.  To me, the fact that you're giving your own blood - a part of yourself - seems very profound, along the lines of organ donation.

I don't think it matters whether blood donation maps to one of the works of mercy.  It clearly is an expression of the second greatest commandment: love your neighbor as yourself.  When you give your life's blood that another may live you are imitating Christ, who gives us his very blood that we might live.  Well done that you are eager to do this.  Here's the Catechism, in case you are interested:

2296 Organ transplants are in conformity with the moral law if the physical and psychological dangers and risks to the donor are proportionate to the good sought for the recipient. Organ donation after death is a noble and meritorious act and is to be encouraged as a expression of generous solidarity. It is not morally acceptable if the donor or his proxy has not given explicit consent. Moreover, it is not morally admissible to bring about the disabling mutilation or death of a human being, even in order to delay the death of other persons.

Blood donation is a triple win because you can 1) save lives without 2) dying yourself and 3) you can do it over and over.  In fact, you can do it multiple ways by donating whole blood, plasma, and platelets.  Everybody who can should be a blood donor (I speak as a five gallon alum).