Great discrepancies occur in the statements of different observers, but inasmuch as each epidemic varies in severity, a severe type of the “Flu” may have a shorter incubative period than a mild type, and therefore taking the variations in type into consideration, may reconcile the differences. If Influenza was accompanied with a facial eruption or exanthem, this would materially assist in the determination of its Incubative period. In Hawaii, two to three days is the most frequent period of Incubation; it may vary, however, from 24 hours to 72 hours, even to five days; in these long incubative cases, headache, aching eyeballs, and great languor are the indicating signs, and those persons so affected succumb slowly and offer great resistance to the overpowering toxins of the Bacillus Influenzae. The Immunity which a person may possess in one Epidemic and not in another, may be accounted for by assuming that each Epidemic may have a difference in the strain or the species of the Influenza bacillus. SALIENT POINTS. Period of Life. Most cases occur between 20 and 40 years. In Schools. The older children are first attacked: open air schools are a positive, but not an absolute defense against Infection. Indoor Schools. The ratio of prevalence amongst children of all ages is 40%. Outdoor Schools. All ages, the ratio of prevalence is 10%. Open Air Occupations. Such as workers in the fields, 12% are attacked. Closed Rooms. Factory Operatives, 49% are attacked. MAIN FACTOR OF SPREAD. Not the Weather, but HUMAN intercourse, especially Commerce; the greater the speed of Commerce, the greater and quicker is the spread of the Flu; it follows the path of HUMAN travel; it is a Contagion solely spread by HUMAN intercourse, viz. “The Influenza Carrier or Carriers.” Positions in life, which require contact with Travelers, necessarily influence and spread the disease. “Flu” is spread in the same ratio of speed as the Carrier of IT. When the Flu is a weakling, his best Nurses and Foster-Mothers are Overcrowding and lack of Pure Air. Where the Crowd is, there the Flu is: little crowding means little Flu; plenty of Crowding, plenty of Flu. QUARANTINE AND ISOLATION. Period of Isolation, for ordinary Flu patients: 12 days. Period of Isolation, for Influenza-Pneumonia cases, until the end of Convalescence. Quarantine and Isolation are beset with difficulties owing to the extraordinary contagious nature of the Flu, due to the multiplicity of Contacts, Carriers, and mild undetected cases. It should be borne in mind that Influenza is a most refractory disease, and not at any time or season is it under our control, and to bring about this condition is as yet an unsolved problem. It may attack us at any time, although its favorite period of appearance is the Autumn and Winter months.