THERAPEUTIC IMMUNIZATION IN MAN 497 



could be successfully inoculated with dust from a room in which a 

 patient lay ; and Josef son states that infection may be acquired from 

 handkerchiefs and other recently handled articles for a short time. 

 Under these conditions it would seem rather likely that the greatest 

 factor in transmission would be found in direct and indirect trans- 

 mission by means of carriers, themselves immune or recently re- 

 covered, harboring the virus and transmitting it to susceptible in- 

 dividuals. And it is possible that many individuals in a community 

 may be immune, owing to mild forms of the disease sustained in 

 childhood which were not recognized as poliomyelitis; for evidence 

 is constantly accumulating that poliomyelitis is not essentially a 

 paralytic disease, that paralysis is merely one of the severe symp- 

 toms, and that mild but immunizing attacks may occur in the form 

 of very slight indispositions, attacks of mild grippe, headache, etc., 

 which under present conditions are not recognized as poliomyelitis. 

 On this basis it would be comprehensible why so often one child of a 

 family is afflicted while others equally exposed are spared. And it 

 would become plain why epidemics sweep through a community se- 

 lecting cases irregularly here and there, and then die out, leaving 

 behind an endemic smoulder of sporadic cases. It would seem as 

 though for the time being all the susceptible children had been 

 afflicted and no further fuel for spread was available. 



Under these conditions the study of contact infection becomes 

 very important, and Frost concludes that none of the other factors 

 usually considered in the spread of an infection, other than personal 

 contact, seems to offer adequate explanation for the spread of epi- 

 demics. To some extent discouraging as far as the contact theory 

 is concerned, the epidemic in New York showed that in 96 per cent of 

 the families afflicted, that is, in 8,287 families, there was one case 

 only to the family, although in these families there were a total of 

 24,883 children. In only 3.6 per cent were there two cases to the 

 family. Just why this should be it is difficult to surmise. However, 

 to some extent this and other radical phenomena in the transmission 

 of this disease may depend upon differences in susceptibility, due per- 

 haps to a light unrecognized attack previously sustained, or to some 

 anatomic or physiological predisposition to infection of the meningeal 

 choroid plexus. In this connection recent studies by Flexner and 

 Amoss 105 are of unusual interest. They find that among the 

 mechanisms that defend the central nervous system from infection is 

 this plexus, which, if in any way injured, becomes unable to function- 

 ate, and in consequence permits infection to pass. The injection of 

 normal monkey or horse serum of isotonic salt solution, or of Ringer's 

 and Locke's solutions, when injected into the meninges, though in 

 itself innocuous, causes a sufficient injury of the membrane to 

 render a subsequently injected lethal dose of virus infectious. 

 105 Flexner and Amoss. Jour. Exp. Med., 1914, XX, 249. 



