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SCIENCE 



[N. S. Vol. L. No. 1292 



full intensity of the epidemic is realized. In 

 the meantime rich, opportunity has been 

 afforded for the free and nnrestricted com.- 

 minglin^ of the sick and the well, of doubt- 

 less healthy carriers of the inciting agent and 

 others, until so high a degree of dissemination 

 of the provoking microorganism has been 

 secured as to expose the entire susceptible ele- 

 ment of the population, which happens to be 

 large, to an almost simultaneous response to 

 the effects of the infecting microbe. 



Deductions of like import can be drawn 

 from the geographical movements of influenza 

 epidemics. In eastern Russia and Turkestan 

 influenza spreads with the pace of a caravan, 

 in Europe and America with the speed of an 

 express train, and in the world at large with 

 the rapidity of an ocean liner; and if one 

 project forwards the outcome of the means of 

 intercommunication of the near future we 

 may predict that the next pandemic, should 

 one arise, will extend with the swiftness of 

 the airship. Moreover, not only is this rate of 

 spread determined by the nature of the trans- 

 portation facilities of the region or the era, 

 but towns and villages, mainland and island, 

 are invaded early or late or preserved entirely 

 from attack according as they lie within or 

 without the avenues of approach or are pro- 

 tected by inaccessibility, as in instances of re- 

 mote mountain settlements and of islands dis- 

 tant from the ocean lanes or frozen in during 

 winter periods. 



It is desirable, in the interest of clear 

 thinking, to carry this consideration of the 

 characteristics of epidemic influenza a step 

 further. A feature of the epidemic disease 

 of particular significance is the tendency to 

 recur, that is, to return to a stricken region 

 after an interval, usually of months, of rela- 

 tive quiescence. Thus the beginnings of the 

 last pandemic in western Europe and the 

 United States have been traced to sporadic 

 cases appearing in April, May and June, pos- 

 sibly earlier even in certain places, while the 

 destructive epidemic raged during September, 

 October and N'ovember of 1918. There are 

 very good reasons for believing that in itself 

 influenza is not a serious disease, but that its 

 sinister character is given by the remarkable 



frequency with which it is followed, under 

 particular circumstances, by a concomitant or 

 secondary pneumonic infection to which the 

 severe effects and high mortality are traceable. 

 Now it is this high incidence of pneumonia, 

 the product of invasion of the respiratory 

 organs with bacteria commonly present on the 

 upper respiratory mucous membranes— strep- 

 tococci, pneumococci, staphyloccocci, Pfeiffer's 

 baciUi, and even meningococci— that stamp 

 the recurrent waves of the epidemic with its 

 bad name. 



If we compare the pneinnonic complications 

 of influenza with those which arose in the can- 

 tonments in 191Y-18, first as attendants of 

 measles and later as an independent infection, 

 we note immediately that in both instances 

 the severe effects and high fatalities arose, 

 not from bacteria brought or imposed from 

 without, but from their representatives which 

 are commonly resident upon the membranes 

 of the nose and throat in health. Whatever 

 we may have to leam of the microorganism 

 inducing measles, still undiscovered, and of 

 influenza, still under dispute, and their mode 

 of invasion of the body, no one would question 

 that the bacteria inducing pneumonia are 

 personally borne. 



With these various considerations before us 

 we may now discuss the question of the 

 efficiency of our public health measures in 

 diminishing the incidence of epidemic dis- 

 eases. It should now be evident that our 

 three examples are essentially instances of 

 respiratory infections, that is, diseases in 

 which the inciting microorganism enters the 

 body by way of the air passages, although not 

 necessarily, as in poliomyelitis, directly in- 

 juring those parts. Protection in diseases of 

 this class is not to be secizred by applying 

 sanitary measures on a wide scale to an ex- 

 traneous and inanimate source of the in- 

 fectious microorganism, as to water supplies 

 contaminated with the dejecta of typhoid 

 patients, or even to inferior animal species, 

 such as the mosquito or the rat, which act 

 as intermediaries in conveying the germs of 

 yellow fever or of infectious jaundice; but it 

 is alone to be attained by methods of personal 



