504 



SCIENCE 



[N. S. Vol. XLIX. No. 1274 



these suppositions are often ingenuous if not 

 convincing. Unfortunately, they seldom stand 

 the test of scientific analysis. 



The weight of evidence now available in- 

 dicates that the immediate cause of the great 

 pandemic of 1918 was an infective virus which 

 passed from person to person imtil it had 

 spread all over the world. The method of 

 spread is believed to have been the same as in 

 other respiratory infections. The reasons for 

 the belief that it was transmitted in this 

 manner lies chiefly in the fact that the pan- 

 demic spread rapidly, and no more so, than 

 people traveled from i>oint to point. 



Nobody so far has positively shown what 

 the virus is, nor how it leaves or enters the 

 body, nor at what period in the disease it may 

 be transmitted to others. Some hold that the 

 Pfeiffer bacillus is the causative agent, others 

 believe that there is a filterable virus which 

 acts independently or in conjunction with the 

 Pfeiffer bacillus. Nearly all agree that the 

 influenza and pneumonia were independent 

 diseases and that the high fatality was due 

 to a very remarkable reduction of resistance 

 to the pneumonia brought about by the in- 

 fluenza. Being of the respiratory type, it is 

 believed that the virus leaves the body by way 

 of the nose and mouth. It is supposed to 

 enter the body by way of the nose, mouth 

 or eyes. 



But, it may be asked, if the influenza and 

 the Pfeiffer bacillus are always with us, why 

 should the disease suddenly become so differ- 

 ent from its ordinary type in respect to sever- 

 ity, infectivity and complications? Nobody 

 has answered these questions. 



There are various ways of replying to them. 

 One is to assume that the infective poison 

 was brought into civilized coimtries from 

 some distant point where it originated. An- 

 other is to suppose that it developed locally. 

 It is not possible to follow these theories 

 through all their details here. The arguments 

 are not convincing by any means. Certainly 

 a complete explanation of the pandemic re- 

 quires a demonstration of how the disease 

 developed wherever that development took 

 place. 



The development of the disease was un- 

 doubtedly a complicated biological phenom- 

 enon. A virus was produced which was 

 capable of overcoming the resistance of a 

 large proportion of those who were exposed 

 to it. Reductions in virulence axe familiar 

 occurrences in connection with infective poi- 

 sons. Controlled attenuations have been at 

 the foundation of a great deal of the best 

 work in immunology since the time of Pas- 

 teur. Increases are less often observed, but 

 it is a well established fact that a virus which 

 has practically lost its pathogenic properties 

 can be exalted to a high state of virulence by 

 inoculating it into susceptible animals. The 

 spontaneous recrudescences of virulent dis- 

 ease in epidemics which sometimes appear to 

 have originated in mild epidemic infections 

 suggest the same process. 



Eeasoning by analogy it would appear not 

 unlikely that an influenza virus which existed 

 somewhere, perhaps among persons who had 

 become accustomed to it and had consequently 

 gained a toleration to it, was introduced 

 among others to whom it was a stranger and 

 who were consequently particularly suscei)- 

 tible to it. This would naturally resiilt in an 

 outburst which might attain pandemic pro- 

 portions. 



The pandemic has shown among other 

 things how widely and how quickly respir- 

 atory infections may travel. It has shown 

 what an enormous interchange of germs takes 

 place in the respiratory apparatus of those 

 who live in cities and towns and villages. It 

 is disquieting to find how readily and fre- 

 quently the bacterial products of the sick gain 

 entrance into the noses and mouths of other 

 persons, but the facts must not be hidden if 

 to acknowledge them will do any good. 



The pandemic calls attention not only to 

 the fact that there is an interchange of mouth 

 germs wherever people meet, but it illustrates 

 how frequently respiratory infections may 

 occur to which little or no attention is given. 

 Some people think that pandemics of colds 

 occur from time to time which are almost as 

 universal as was the recent influenza. Their 

 pandemic character is not suspected because 



