SECOND LECTURE. 



IMMUNITY. 



BY GEORGE M. STERNBERG, M.D., LL.D. 

 (Surgeon-General U. S. Army, Washington, D. C.) 



The resisting power, natural or acquired, which living 

 animals possess against invasion by pathogenic micro-organ- 

 isms is commonly spoken of as "immunity." But we might 

 include in our definition of the term, used in the biological 

 sense which we shall attach to it in the present lecture, the 

 more general resisting power which living animals possess 

 against saprophytic bacteria. It is hardly necessary to call 

 attention to the fact that, under suitable conditions as to tem- 

 perature and moisture, dead animal tissues undergo putrefac- 

 tive decomposition, — i.e. are invaded by saprophytic bacteria, — 

 while healthy, living animals resist such invasion. This more 

 general immunity appears to be due to causes which are the 

 same or similar to those which enable insusceptible animals 

 to resist invasion by pathogenic bacteria. There is also an 

 immunity, which the Germans designate '' giftfcstigimg,'' which 

 is manifested by an increased resisting power to the toxic 

 action of the chemical products of pathogenic bacteria, and 

 which may be established by introducing these toxic substances 

 into susceptible animals quite independently of the micro- 

 organisms which produce them — inoculations with filtered 

 or sterilized cultures. This corresponds with the acquired 

 immunity which has been shown to result from the inoculation 

 of susceptible animals with non-lethal doses of certain toxic 

 albuminous substances of animal and vegetable origin, — snake 

 poison, abrin, ricin, etc. 



