Abstract: A diagnostic agent for the detection of occult blood in feces comprising hydrogen peroxide and, as a chromogen, guaiaconic acid A, optionally with a stabilizer. The invention provides, as a novel substance, guaiaconic acid A having a specific extinction E.sub.1 cm.sup.1% at 600 nm of at least 200, determined by the reaction with peroxidase and hydrogen peroxide, having infra-red bands at1600 cm.sup.-1 (m);1505 cm.sup.-1 (v.s.);1260 cm.sup.-1 (s;b);1115 cm.sup.-1 (m);1025 cm.sup.-1 (m); and1200 cm.sup.-1 (s;b)and having an R.sub.F value of 0.45 (toluene/dioxan/glacial acetic acid; 90:25:10 v/v/v).

Abstract: A device for the uniform dosing of an amount of faeces onto reagent paper for the detection of a component material in the faeces. The device comprises test paper and a template disposed thereover having a given thickness and comprising at least one set of two superposed openings of any desired shape. Each set of openings includes a first opening and a second opening disposed between the first opening and the test paper and having a larger area than and encompassing the area of the first opening.