A striking difference between the two types of waves of influenza is the uniformity and relative constancy of the primary type as contrasted to the great variation in the secondary type. The story of the first spread of influenza in one community is usually similar to that of its spread in any other community. Certain exceptions will be alluded to later. But in the case of recurrent epidemics we may find them more severe or much milder; we may find that they attack a large number of individuals or a very few; we may even find an entire absence of recurrent epidemics in certain communities. The primary curves are relatively uniform; the secondary curves are variable. Between 1889 and 1894 in England there were four epidemics. The first was primary, symmetrical, and lasted between December and February, 1889–90. The second was asymmetrical and much more fatal in the localities studied by Greenwood. It occurred in the spring and summer of 1891. There was a third epidemic in the autumn and winter of 1891–92 and a fourth occurred from November, 1893 to January, 1894. The third epidemic, according to Greenwood, showed some tendency to revert to the primary type in respect to symmetry, while the fatality rate partook of the character of a secondary epidemic. Creighton writes: “That which chiefly distinguishes the influenza of the end of the nineteenth century from all other invasions of the disease is the revival of the epidemic in three successive seasons, the first recurrence having been more fatal than the original outbreak, and the second recurrence more fatal (in London at least) than the first. The closest scrutiny of the old records, including the series of weekly bills of mortality issued by the parish clerks of London for nearly two hundred years, discovers no such recurrences of influenza on the great scale in successive seasons.” Greenwood, who has studied this subject in great detail in England, discusses Creighton’s remarks as follows: “He would be a bold man who challenged the accuracy of Creighton upon a point of historical scholarship, and I have only to suggest that there are faint indications of increased mortality in years following primary epidemics of influenza prior to the nineteenth century. Thus 1675 was a year of primary epidemic influenza, fully described in Sydenham’s Observationes Medicae. “The nature of the succeeding constitutions is not clear, but the deaths ‘within the bills’ for 1676 were considerably more numerous than in 1675, although smallpox, fever and ‘griping of the guts’ were noticeably less fatal.