The Nazis went to great lengths to determine Germans who had pure Aryan descent in order to ensure a pure German nation. All kinds of criteria was used including caricatures showing Jewish types and the testing of pure Aryans by determining their genealogical Aryan purity. This was for the express purpose of weeding out Jewish or other non-pure Aryan blood. For example, Germans wishing to join the Nazi party had to undergo rigorous questioning to determine their genealogy.
These documents show the methods used by the Nazis to exclude German Jews from all facets of German society. They were used to determine that an applicant for the Nazi party was a full blooded German whose parents and grandparents were also pure Germans. To join the SS, one had to fill out an additional document going back to great great grandparents to determine a pure blood German. These documents show the extent to which the Nazis tried to foster a pure blood Aryan race.
Sources: Yad Vashem