Studies on T H E Nature of T H E Virus of Influenza I. the Dispersion of the Virus of In]?liyenza a in Tissue Emulsions and in Extra-embryonic Fluids of the Chick by Leslie

While certain properties of the influenza virus have been inferred from numerous immunological and epidemiological studies published in recent years, little definite information as to its physical nature has been obtained. Elford, Andrewes, and Tang (1), as a result of ultrafiltration studies of mouse lung emulsions, concluded that the infectious agent has a diameter of 80 to 120 m/z. Eftord and Andrewes obtained a value of 87 to 99 m# by eentrifugation (2). This relatively high order of size was supported by Hoyle and Fairbrother (3) when they were able to sediment most of the infectivity from tissue emulsions by the use of a centrifuge running at a speed of 15,000 R.P.M. They observed particles of the indicated size range by dark field examination of the infectious sediments. Recently it has been shown that the allantoic and amniotic fluids from 10 to 12 day chick embryos inoculated with porcine strains of influenzal virus gave high infectivity titers in spite of their low protein content (4). The same was observed for the human strains of influenza A simultaneously by several investigators (5-7). Preliminary studies of these fluids have led us to the conclusion that the size of the virus may be much smaller than believed heretofore, a tentative estimate of the diameter being 10 m# or less (8, 9). The analytical diffusion method employed by Bourdillon (10) on mouse lung virus indicated that a very small amount of the infectivity is carried by particles having a diffusion constant corresponding with that of a spherical body as small as 6 m# in diameter. The same technique applied to the infected extra-embryonic fluid showed a very large proportion, as much as haft, of the pathogenic material to be associated with 6 m# particles. Additional studies have been undertaken both on the virus present intissue emulsions, and on that in the egg fluids. These have confirmed our original surmise that the size of the infectious unit is only a small fraction of that indicated by former studies (1-3), and have led to certain successful purification procedures. This paper contains the results of a study of the dispersion of the influenza