Magen David Adom, whose blood supplies dip dangerously when temperatures rise, has decided to collect blood from donors on Fridays as well. The fact that so many Israelis are on summer vacation during the coming months means that the supply of Type O blood and RH- blood of all types causes elective operations to be postponed and harms ongoing medical activities in the hospitals. Blood donation rooms at MDA stations around the country will be open Fridays during the summer. All donors receive blood insurance for themselves and their immediate family. More details can be obtained by calling 1-800-400-101 or going into the Web site at www.mdais.org. Groups of 20 or more blood donors can invite an MDA bloodmobile to come by calling (03)5300402.