Dr. Wyatt's second notebook to be titled Nucleic Acids, written during his time at the Virus Research Unit, Molteno Institue, Cambridge, England. Within this notebook are Dr. Wyatt's procedures and calculations to estimate the mean ratios of bases in the nucleic acids of ram sperm and calf thymus. The book contains the ultra violet spectra of the proposed methylcytosine extracted from nucleic acids of herring and ram sperm and a comparison of this data is made with UV spectra of synthetic 5-methylcytosine obtained from Mr. A. Pircio of Fordham University. This data provides the evidence for Dr. Wyatt's1950 Nature paper on the "Occurrence of 5-Methyl-Cytosine in Nucleic Acids". Also in this book are notes on Dr. Wyatt's experiments on samples of DNA from earthworms, yeast, locusts, mushrooms, echinoderms and moths. The back of the book contains standard absorption data for use with UV spectra.