Febbuaby 12, 1909] 



SCIENCE 



247 



but there are many striking exceptions il- 

 lustrated well by the now familiar " ha- 

 cillus carrier." The body may overcome 

 the disease but not the cause, which may 

 persist in spite of the increase in anti- 

 bodies. The disease subsides, the dis- 

 turbances are smoothed away, and yet the 

 germ lives on in the host, apparently harm- 

 less and unharmed, sometimes for remark- 

 ably long periods. But the equilibrium is 

 not always a stable one; the immunity of 

 the host may give way and recurrence 

 develop ; or the resistance of the germ may 

 weaken and eventually complete destruc- 

 tion and final elimination take place. 



Germs isolated from typhoid and 

 cholera carriers have been found in some 

 cases to offer special resistance to anti- 

 bodies, including opsonins, but the mech- 

 anisms of this mutual immunization of 

 microbe and host are still obscure, and on 

 account of the self-evident and tremendous 

 importance of the carrier in spreading 

 disease they invite special study. 



At this point I may recall that the re- 

 lapses in relapsing and related fevers are 

 now ascribed to the survival in each attack 

 of a few spirilla which, having become im- 

 mune to the antibodies of the host, give 

 origin to new "serum-fast" strains that 

 continue the relapses. 



Exceedingly interesting conditions are 

 found in certain chronic infections of the 

 urinary tract with bacilli of the colon 

 group, the indications being that the in- 

 fecting bacillus may partially immunize 

 itself, in one case to the lysin, in another 

 to the opsonin, in the patient's blood, or 

 that the amounts of different antibodies 

 vary greatly in the different cases. 



In Metchnikoff's original doctrine of 

 phagocytosis in infectious diseases a fun- 

 damental tenet reads that as a microbe 

 grows in virulence its resistance to phago- 

 cytosis increases. Recent experiments 

 give results in complete harmony with this 



teaching. On analysis the resistance of 

 certain highly virulent bacteria to phago- 

 cytosis is found to depend on insusceptibil- 

 ity to opsonic action, owing apparently to 

 lack of affinity for the opsonin. As pneu- 

 mococei, streptococci and other bacteria on 

 successive passages through suitable ani- 

 mals become more and more virulent for 

 these animals, they at the same time ac- 

 quire a parallel increase in resistance to 

 phagocytosis. When cultivated outside 

 the body reversion readily takes place to 

 less virulent states, associated with a re- 

 turning afSnity for opsonin and an in- 

 creasing susceptibility to opsonic action. 

 Investigating this property of pneumo- 

 cocci to develop such strong defense 

 against phagocytosis, Rosenow found that 

 extraction or autolysis of virulent pneu- 

 mococei brings into solution a substance or 

 group of substances that neutralize the 

 pneumococco-opsonin in human serum, but 

 not other opsonins. After extraction of 

 this substance, which is thermostable and 

 insoluble in alcohol or ether, virulent 

 pneumococci unite with opsonin and be- 

 come phagoeytable, while avirulent pneu- 

 mococci on treatment with extracts of 

 virulent strains not only become resistant 

 to phagocytosis in the test-tube, but also 

 to some degree virulent for animals. 



Entirely independently, Tchistovitch 

 and Yourevitch appear to have reached 

 identical results on all points, except that 

 they did not study the virulence of aviru- 

 lent pneumococci after treatment with 

 extracts of virulent strains. 



We may say then that the properties 

 called virulence in pneumococci appear to 

 depend, to a very large extent, if not 

 wholly, on the formation of an actual sub- 

 stance — "virulin"^ — which may be ex- 

 tracted and studied by itself. It is hoped 

 that this demonstration may prove a basis 



' " Antiphagin " — Tchistovitch and Yourevitch. 



