During his time at Columbia, Chargaff published numerous scientific papers, dealing primarily with the study of nucleic acids such as DNA using chromatographic techniques. He became interested in DNA in 1944 after Oswald Avery identified the molecule as the basis of heredity. Cohen says that "Almost alone among the scientists of this time, Chargaff accepted the unusual Avery paper and concluded that genetic differences among DNAs must be reflected in chemical differences among these substances. He was actually the first biochemist to reorganize his laboratory to test this hypothesis, which he went on to prove by 1949." Chargaff said of the Avery discovery: "I saw before me (in 1944), in dark contours, the beginning of a grammar of biology", and in 1950 he published a paper with the conclusion that the amounts of adenine and thymine in DNA were roughly the same, as were the amounts of cytosine and guanine. This later became known as the first of Chargaff's rules. Instrumental in his DNA discoveries were the innovation of paper chromatography, and the commercially-available ultraviolet spectrophotometer tool.