314 BACTERIOLOGY. 



cated human tuberculosis, but does bring about 

 a reaction in the case of mixed infections oc- 

 curring in the form of inflammation of the 

 lungs by stimulating the pneumonically infil- 

 trated parts. According to Romer it is possible 

 to employ in the place of tuberculin and also 

 of mallein the proteids produced by many diffe- 

 rent kinds of bacteria. Certain proteids, there- 

 fore, act as powerful stimuli and in such a way 

 that active proteid bodies of a kind to be men- 

 tioned presently, and which are possessed of 

 bactericidal and antitoxic power, make their 

 appearance in the blood in greater abundance 

 than before ; such proteids are not themselves 

 the specific protecting substances. 



In this discussion it is of practical advantage 

 to distinguish between natural* resistance or 

 immunity, acquired immunity (gained either 

 naturally or artificially) and the habituation 

 to or tolerance of poison. In natural immunity 

 microbes and parasites can not invade the body 

 of the organism ; the body possesses the power 

 of destroying the parasites and their poisons. 

 In specifically acquired immunity the body 

 has gained the power of preventing the inva- 

 sion of certain definite parasites and their for- 

 mation of poison, although before the acquisi- 

 tion of this property these germs were able to 

 enter the body and do harm. In a state of 



