In order to identify an organism after isolation, tube, plate, and other cultivations must be prepared, incubated under suitable conditions as to temperature and environment, and examined from time to time (a) ~macroscopically~, (b) by ~microscopical methods~, (c) by ~chemical methods~, (d) by ~physical methods~, (e) by ~inoculation methods~, and the results of these examinations duly recorded. It must be stated definitely that no micro-organism can be identified by any _one_ character or property, whether microscopical, biological or chemical, but that on the contrary its entire life history must be carefully studied and then its identity established from a consideration of the sum total of these observations. In order to give to the recorded results their maximum value it is essential that they should be exact and systematic, therefore some such scheme as the following should be adhered to; and especially is this necessary in describing an organism not previously isolated and studied. SCHEME OF STUDY. Designation: Originally isolated by (_observer's name_) in (_date_), from (_source of organism_). ~1. Cultural Characters.~--(_Vide_ Macroscopical Examination of Cultivation, page 261.) Gelatine plates, } Gelatine streak, } at 20°C. Gelatine stab, } Gelatine shake, } Agar plates, } Agar streak or smear, } Agar stab, } Inspissated blood-serum, } at 20° C. and 37°C. Bouillon, } Litmus milk, } Potato, } Special media for the purpose of demonstrating characteristic appearances. ~2. Morphology~.--(_Vide_ Microscopical Examination of Cultivations, page 272.) Vegetative forms: Shape. Size. Motility. Flagella (if present). Capsule (if present). Involution forms. Pleomorphism (if observed). Sporing forms (if observed). Of which class? Staining reactions. ~3. Chemical Products of Growth.~--(_Vide_ Chemical Examination of Cultivations, page 276.) Chromogenesis. Photogenesis. Enzyme formation. Fermentation of carbohydrates: Acid formation. Alkali formation. Indol formation. Phenol formation. Reducing and oxidising substances. Gas formation. ~4. Biology.~--(_Vide_ Physical Examination of Cultures, page 295.) Atmosphere. Temperature. Reaction of nutrient media. Resistance to lethal agents: Physical: Desiccation. Light. Colours. Chemical germicides. Vitality. ~5. Pathogenicity:~ Susceptible animals, subsequently arranged in order of susceptibility. Immune animals. Experimental inoculation, symptoms of disease. Post-mortem appearances. Virulence: Length of time maintained. Optimum medium? Minimal lethal dose. Exaltation and attenuation of virulence? Toxin formation.