ï~~440 EPIDEMIC INFLUENZA that time not a single case of the epidemic type of influenza had occurred in Finland. In numerous instances the filiation of case withcase has been clearly traceable. ThephyiElas and nursesattending the firstiAiported patients, the imediate membeir of the househod1 9oif ertadthein oime remote relatives, the barracks associates of soldiers retirni'ngrgfom leave, those persons having business on-15r d a;vessel arriving with influenza patients on board, are always among the first to be attacked Cfjp.2-57-259); Dopter and de Lavergne 1925, pp. 553-5; Friedrich 1894, p. 4). Nothing, in factisetterestablished than the importance T iiman agent in spreadingjnfluenza. Whenthe- attempt is made, ho nezer particularize the mode of transilssiohIthere is room for debate. Two ways in which the iifluenza virus might conceivably be distributed have been extensivelydiscussed: (A) infectious droplets aii4 (B ( indirect.conta3P15c aiids or eating utensil. A. INFECTIOUS DROPLETS Analogy with other diseases in which the respiratory tract is especially involved has inclined many writers. to acept-4t.e hypothesis th amnb hpry Jxthe chief means by whicinfluenza is disseminated. Certainly this explanation is quiteJinacerd-with the observed facts of epidemic spread. The prevailing opinion is clearly expressed by V. C. Vaughan (1922, p. 370) who says: "There is little doubt that influenza is spread from person to person through ouging, sneezing, laughing and ar-ingor byhee- en-n-which make possible-thc.dcirec trashct ex fre imaterial from the mouth and nose.of hein ected person to the nasopharynx of the hitherto uninfected'7~ Two main difficulties have prevented the universal. and speedy acceptance of this view. It seems likely that some measure of uncertainty will continue to exist until (1) the localization of the influenza virus in the body of the patient can be quite definitely determined and (2) successful transmission experiments can be carried out. Neither of these requirements has been satisfactorily met. Lack of knowledge prevented in 1918-and still prevents-the use of any rapid and certain laboratory procedure for determining the location of the virus in. the mouth or nose or any other part of the body. F i i 1 { TRANSMISSION 441 Owing to the natural insusceptibility of the lower animals to influenza infection,.animal experimentation has not yielded decisive results. The careful experiments of Wherry and Butterfield (1920) showed that when white mice, white rats and guinea-pigs were exposed to finely divided influenza sputum sprays some died of a primary pneumonia, and others of a general infection due to a strain of Bacillus enteritidis. The results indicated to the authors that something in the sputum-sprays produced a change in the pulmonary tissues favoring secondary localization of a Bacillus enteritidis strain resident in the host. Attempts to transmit influenza to healthy nonimmune human volunteers have been singularly fruitless. Probably the most carefully planned and conducted experiments in this field have been those carried out under the auspices of the U. S. Public Health Service (Rosenau, Keegan, Goldberger and Lake 1921; McCoy and Richey 1921; Rosenau, Keegan, Richey, McCoy, Goldberger, Leake and Lake, 1921; cf. also, Rosenau 1919; Leake 1919). In the first series (Boston, November-December, 1918) stt '-=-volunteers rangingfror15to:34 years of agewere tliesiibjects, thirty-niff wifhno history of havfiigh{ia uiiuenza at any time, although apparently some degree of=exposure had occurred. A variety of inoculation.e thQd4s was employed: filtered and unfiltered secretions fromp the upper respiratory tract of patients with typical influenza were sprayed into the nose and throat anThdiittled into the eyes; direct swabbing from nasopharynx' to nasopharynx was resorted to; in one experiment freshly drawn citrated-blood-wes-injected-subcutaieouily. The results were thus summarized: "In only one instance was any reaction observed in which a diagnosis of influenza could not be excluded, and here a mildly inflamed throat seemed the more probable cause of the fever and other symptoms. Nothing like influenza developed in the other volunteers". In spite of these remarkable negative results the writers conclude that "it is nevertheless probable that the disease is transmitted by the discharges from the mouth and nose" The second series was carried out during the same period, but in another locality (San Francisco, November-December, 1918). The experiments were con 0