THOMAS M. RIVERS 523 



of as "inclusion bodies."' In this respect many virus diseases differ from those caused 

 by ordinary bacteria. 



IMMUNITY TO FILTERABLE VIRUS DISEASES 



With a few exceptions, diseases produced by the filterable viruses, if recovered 

 from, lead to a lasting immunity. In this respect virus diseases differ from those 

 caused by the better-known bacteria. This is not universally true, however, since one 

 attack of typhoid fever produces in the recovered individual a fairly lasting immunity. 

 Many questions have arisen in regard to this kind of immunity, but so far they have 

 not been satisfactorily answered. Nevertheless, a few of the possibilities will be dis- 

 cussed. 



In the first place, it is possible that the lasting immunity is due to repeated infec- 

 tions so mild that they attract no attention except in the initial instance. In regard 

 to diseases as prevalent as measles and chicken-pox this might serve as an explana- 

 tion. On the other hand, one can hardly explain the persistent protection against pol- 

 iomyelitis and smallpox upon such grounds. Another possible explanation for the 

 lasting immunity is that it is due to a prolonged sojourn of the virus in the body, or 

 perhaps to its persistence in an individual once infected. Winkler,' in his review of im- 

 munity to vaccine virus, suggests this possibility. When confronted with the idea one 

 invariably says that it is impossible, because, if it were true, everyone would spread 

 measles and chicken-pox. This would not necessarily be the case, however. Typhoid 

 bacilli have been found in the walls of gall-bladders many years after attacks of ty- 

 phoid fever. Furthermore, when the mucous membranes lining the gall-bladders are 

 normal, there is little danger of the disease being spread by these carriers. Most hu- 

 man beings carry tubercle bacilli, but only a few spread tuberculosis. Individuals 

 harboring Treponema pallidum are not always infectious, particularly in the latent 

 stages of syphilis. Furthermore, syphilis is an excellent example of a disease in which 

 there is a persistent infection coincident with a refractory state in the host to rein- 

 fection. For information concerning discussions of this paradox one should read 

 Chesney's review, "Immunity in Syphilis."'' 



In regard to virus diseases, is there any evidence (i) of a prolonged or persistent 

 infection, (2) of a coexistence of infection and refractory state in the host to reinfec- 

 tion from without, and (3) of a causal relation between the prolonged or persistent 

 infection and the lasting immunity? There is considerable evidence-t that a pro- 

 longed infection occurs in some virus diseases and also that this infection can persist 

 for a long time in a host refractory to reinfection, e.g., Cole and Kuttner^ have 

 shown that the "salivary-gland virus" of guinea pigs can be obtained at will from 

 immune pigs, and in this particular instance it appears that a pig once infected con- 



■ Findlay, G. M., and Ludford, R. J.: Brit. J. Ex per. Path., 7, 223. 1926; Lipschiitz, B.: Seuchen- 

 hckdmpfiing, 3, 79. 1926. 



= Winkler, W. F.: Ergehn. allgem. Path. u. path. Anat., Abt. I, 21, 45. 1925. 

 ^Chesney, A.: Medicine, 5, 4.63. 1926. 



-i Cole, R., and Kuttner, A. G.: /. Exper. Med., 44, 855. 1926; Lipschiitz, B.: von Prowazek's 

 Handb. d. path. Prot., i, 230. Leipzig. 191 2. 

 sCole, R., and Kuttner, A. G.: loc. cit. 



