204: TRANSACTIONS OF THE [MARCH 2^^ 



Mr. Lucius Pitkin read a paper on 



THEORIES concerning THE PROTECTIVE INFLUENCE OP MITI- 

 GATED VIRUS. 



In introducing the discussion of this tlieme, it may be useful 

 to define, for those not conversant with tlie subject, the terms- 

 ''virus" and "mitigation/' and also wliat is meant by "protec- 

 tive influence." The term "virus" is used in this paper as 

 synonymous with disease-producing micro-organism, and while- 

 the contagium of all infectious diseases is not as yet jiroven to- 

 be of this character, still in some six or seven the proof is abso- 

 lute, and only such will be used as exami)les. 



Mitigation can be defined as such a modification of the disease 

 germ that its inoculation into a susceptible animal will produce 

 a disease very much milder tluin the original fdrm — sometimes 

 an almost imperceptible teni})orary effect. The degrees of miti- 

 gation are numberless, varying from almost the original viru- 

 lence to the germ totally innocuous. Tlie methods of mitiga- 

 tion, Avhile numerous, all de]iend u])on surrounding the germ 

 with unfavorable environment, so that its vitality is lowered^ 

 That animals susceptible to anthrax lose in a majority of cases 

 this susceptibility by inoculation Avith mitigated virus,, is no- 

 longer a question, l^he same is true in regard to the cholera of 

 fowls. The facts are undisputed. The method has its dangers, 

 and may be found inexpedient. The protective influence may 

 not be so permanent as believed by some of its advocates, but 

 with that we are not now concerned. The sole object of tliis 

 paper is to critically examine the theories which have beei> 

 brought forward to explain the " wherefore ^'' of the i)rotective 

 influence which has been ])roved to exist. 



It is obvious that, besides the phenomenon of protection by 

 mitigated virus, there is a correlated ])henomenon which must 

 likewise be explained by any theory, and this is the protectiou 

 afforded in many cases by a previous attack of the same disease^ 

 This, however, is easily met by all the theories, since a previous 

 attack, on the germ theory of disease, is in reality equivalent to- 

 inoculation with a virus not sufficiently powerful to kill. An 

 interesting question, which lias suggested itself, is the immunity 

 of an individual to a particular disease after suffering from some- 

 other disease. Had we the liistory of enough individuals, wo 

 would possibly find, on tabulating the statistics, that the occur- 

 rence of a special disease had protected in a considerable degree 

 against some other disease, not, perhaps, to tlie degree noticed 

 in protection from subsequent attacks of the same disease, but 

 enough to clearly show in the average a protective influence. 



