At the same time Barlow cooperated with Prof. Salvador Mateos Higuera in a descriptive study of Mexican codices. Within a brief three years he had cooperated with George T. Smisor to plan and edit "Tlalocan", a journal of source materials on native cultures of Mexico. Beginning in 1943 with the appearance of "Tlalocan" his productivity attained added momentum and his articles appeared with increasing frequency in the scholarly journals of Mexico, United States and Europe. Concern for minutiae led to such works of detail as "The 18th Century "Relaciones Geograficas"".