314 



SCIENCE 



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



seems imi)erative ttat we should consider not 

 only tlie sum of our knowledge of epidemics, 

 but also certain facts relating to the popula- 

 tion affected, whicli react powerfully on the 

 successful application of the hygienic means 

 available. 



Three epidemic diseases, poliomyelitis, strep- 

 tococcus pneumonia and influenza, have been 

 especially destructive in the western world 

 during the past three years; also, because of 

 certain common characteristics, they are well 

 adapted for the purpose I have in view. 



In the United States we are becoming in- 

 creasingly familiar with epidemics of polio- 

 myelitis. Prior to 1907 infantile paralysis 

 was a rare disease in this country; since then 

 it has prevailed fitfully every summer and 

 autumn, and in one notable instance, at least, 

 in the winter season,- claiming victims by the 

 score or hundred, imtil in 1916 an outbreak of 

 unprecedented severity, with its center of vio- 

 lence in New York state, swept over a con- 

 siderable number of states. 



Fundamental knowledge of poliomyelitis 

 may be said to have grown rapidly since Wick- 

 man's epochal clinical studies published in 

 1907. We are indeed to-day in possession of 

 precise information covering essential data 

 with regard to the nature of the inciting 

 microorganism, notwithstanding its very mi- 

 nute size, and also concerning the manner in 

 which it leaves the infected or contaminated 

 body within the secretions of the nasopharynx 

 chiefly and gains access to another human 

 being by means of the corresponding mucous 

 membranes and apparently no other way. 

 Moreover, the inciting virus so called, up to 

 the present time and notwithstanding many 

 and assiduous efforts, has not been detected 

 apart from the infected or merely contami- 

 nated human being, and there is therefore no 

 fo^^ndation in ascertained fact for an assump- 

 tion that the virus is conveyed to persons 

 otherwise than by other persons who harbor it. 



The second example, namely, that of strep- 

 tococcus pneumonia, presents a phenomenon 

 almost, if not quite, new among the epidemic 

 diseases. It appears as if during the winter 

 of 1917-1918 there occurred in several locali- 



2 Fairmont, West Virginia. 



ties within the United States and also, but in 

 less degree, in France, at least a great increase 

 in the incidence of a type of pneumonia which 

 previously had been very infrequent. It ap- 

 pears also that the greatest number of cases 

 and of fatalities arose in the United States in 

 the military cantonments; that the disease 

 first prevailed as a secondary pneumonia fol- 

 lowing measles ; but that before long the sever- 

 ity of the infection was such that cases of 

 primary streptococcus pneumonia began to 

 arise. Moreover, at this juncture the disease 

 spread from the military to the civil popu- 

 lations. 



The nature of the microorganism inducing 

 this form of epidemic pneumonia is indicated 

 in the name which the disease has come to 

 bear. The difficulty in this instance has not 

 been in finding out the inciting microbe, but 

 rather in differentiating the streptococci re- 

 sponsible for the epidemic disease from strep- 

 tococci possessing the ordinary pathogenic 

 properties, or even from those of saprophytic 

 nature so commonly present on the upper 

 respiratory mucous membranes without pro- 

 voking widespread disease. However, niuner- 

 ous studies of the bacteriology of this epi- 

 demic of pneumonia, at distinct and often 

 widely remote cantonments, showed that the 

 mierobic incitant was in almost every instance 

 Streptococcus hemolyticus. Moreover, because 

 of the wide occurrence of the epidemic pneu- 

 monia, this type of streptococcus could be 

 found in normal throats and as a secondary 

 invading microorganism in the lungs in cases 

 of ordinary lobar pnemnonia. Thus far very 

 little progress has been made in the classifica- 

 tion of streptococci, which form a class ap- 

 parently even more heterogeneous than the 

 pneumococci. 



The point I wish to emphasize is this: 

 Regarding epidemic diseases in general we 

 are wont to assume the introduction from 

 without and usually from a distant locality 

 of a special kind or race of microorganism 

 which is held directly responsible for the epi- 

 demic ensuing. In the instance of the epi- 

 demic pneumonia no such importation or new 

 introduction of the inciting streptococcus 

 needs to be or actually is assumed. It is so 



