I never saw this information about using saliva to remove blood stains until I published it in my own book, Straight Talk About Quilt Care I and now available as Vol. II (an e-book) sold on amazon or my website. It is a tip I learned from a costume designer friend who had worked on off-Broadway shows. She explained that the enzymes in one's OWN saliva will dissolve fresh blood. It is always good to swab cotton surfaces with cold water, after the fact. The method sounds gross but is the most effective and expedient manner to do this.
My best,
Patricia Lynne Grace Cummings, Quilter's Muse Publications