524 FILTERABLE VIRUSES 



tinues to harbor the virus indefinitely in spite of a refractory state to reinfection from 

 without. The question as to whether the lasting immunity is dependent per se upon 

 a prolonged sojourn or persistence of viruses in the body cannot be answered at the 

 present time. Nevertheless, such an idea, novel in regard to virus diseases, is worthy 

 of serious consideration. 



Another interesting feature concerning immunity to virus diseases is the fact that 

 it is doubtful, with a few exceptions, whether injection of a virus completely inacti- 

 vated leads to a protection against the same virus in an active state. Furthermore, vi- 

 rucidal properties do not appear in the serum of naturally resistant animals which 

 have received repeated injections of active virus. Therefore, it seems that an actively 

 acquired immunity and evidences in the serum of such an immunity are dependent in 

 some way upon an actual infection with the virus, even though it be so mild at times 

 as to give rise to no symptoms. 



The degree of active immunity usually exhibited by individuals recovered from 

 virus diseases seems disproportionate to the amount of passive protection afforded by 

 their sera. This fact has led many observers to believe that the protection against 

 virus diseases is predominantly a tissue immunity rather than a humoval one. Be that 

 as it may, protective substances do occur in the sera of individuals who have re- 

 covered from certain virus diseases. Furthermore, virucidal properties, precipitins, 

 and complement-fixing antibodies have also been demonstrated in the sera of these 

 individuals.^ 



GENERAL REVIEWS AND DISCUSSIONS 



Bayon, H. P.: /. Trop. Med., 29, 17. 1926. 



Doerr, R.: Centralbl. f. BaktcrioL, Abt. I, Ref., Beih., 50, *i2. igii. 



Kraus, R.: Med. Klin., 22, 540, 579. Berlin, 1926. 



Loeffler, F.: Centralbl. f. BakterioL, Abt. I, Ref., Beih., 50, *i. 1911. 



Lucksch, F.: Prag. tierdrztl. Arch., Teil A, 5, 83. 1925. 



MacCallum, W. G.: Medicine, 5, 59. 1926. 



Roux, E.: Bull. deVInst. Pasteur, i, 7, 49. 1903. 



Twort, F. W.: /. State Med., 31, 351. 1923. 



Wolbach, S. B.: /. Med. Research, 27, i. 1912. 



' Gordon, ISI. H.: Med. Research Conn., "Spec. Rep. Ser.," No. q8. London, IQ25. 



