I. General.- A. Abbreviations and Expressions Frequently Used.- B. Basic Equipment for the Experiments.- C. Calculation of Titers and Some Statistical Methods.- D. Technical Literature.- II. Experiments and Problems.- A. Phage Growth and Ultracentrifugation.- 1. Large Scale Production of Phage T4.- 2. Purification and Concentration of Phage T4.- a) Dextransulfate - PEG Two-Phase Technique.- 3. Purification and Concentration of Phage T4.- b) Centrifugation with and without CsCl.- 4. Determination of the Density of Phages by CsCl Gradient Centrifugation.- 5. Estimation of Sedimentation Constants by Sucrose Gradient Centrifugation 43 Problems.- B. Nucleic Acids and Transcription.- 6. Isolation of DNA from T4 or T5 Phages.- 7. Thermal De- and Renaturation of DNA from Different Organisms.- 8. Isolation of 3H-Uridine-labeled mRNA from Bacteria Infected with T4.- 9. Hybridization of Phage-DNA and Phage-mRNA on Nitrocellulose Filters.- 10. Time of Gene Transcription - Determined by Phenocopying with 5-Fluorouracil 72 Problems.- C. Mutation and Photobiology.- 11 Genotype and Phenotype.- 12. Proof of the Random Distribution of Spontaneous Mutations.- 13. Mutagenic and Inactivating Action of Ultraviolet Light on Phage Kappa.- 14. Reversible Photochemical Alteration of Cytidylic Acid.- 15. Chemical Induction of Forward and Back Mutations in Bacteria.- Problems.- D. Transfer and Recombination of Genetic Material.- 16. Conjugation of E. coli Bacteria.- 17. Two- and Three-Factor Crosses with Phage Kappa.- 18. Transduction of Linked and Unlinked Genetic Markers with Phage P1.- 19. Transfer and Elimination of a Plasmid (F'lac).- 20. Induction of Lysogenic and Bacterio-cinogenic Bacteria.- 21. Transfection of E. coli Spheroplasts with DNA of Phage Lambda.- Problems.- E. Phenotypic Expression.- 22. Determination of a Metabolic Block by Auxanography and Syntrophy.- 23. Complementation of Nonsense Mutants of Phage Kappa 1.- 24. Constitutive and Induced Synthesis of ß-Galactosidase.- 25. The Morphopoesis of T4 Phages.- Problems.- III. Appendix.- A. Nutrient Media and Solutions.- B. Strains of Bacteria and Phages.- C. Sources of Supplies for Experiments.- D. The Recording of Scientific Experiments..- IV. Experimental Results and Answers to the Problems.- A. Experimental Results.- B. Answers to the Problems.- The Genetic Code.