128 CONTEMPORARY SCIENCE 



Thus we have learned that the immunity reactions, or 

 the effects on bacteria and their poisons, of the fluid and 

 cells of the body as modified by the process of artificial 

 immunization, provide more delicate and precise means of 

 discriminating bacterial species than the 'qualities of form, 

 growth appearances and physiological activities, and more 

 accurate methods of distinguishing poisons than the most 

 refined chemical analyses ; and we shall learn a little later 

 in connection with the distinct but related hypersensitive 

 or anaphylactic state, that the prepared and sensitized 

 animal body responds to infinitesimal amounts of protein 

 matter according to its specific origin, in a manner not 

 otherwise determinable and far beyond the most delicate 

 laboratory test which the chemist has invented. The ani- 

 mal body thus artificially prepared, or as sometimes hap- 

 pens naturally sensitive, acquires an appreciation of the 

 inner constitution of the protein molecule, classifying it, 

 as it were, not only according to its ordinary chemical 

 nature, but according to its species origin. 



The immunity reactions we have considered are not 

 artificial creations, since as we now know, they are the 

 very processes which nature employs in her unaided ef- 

 forts to abate infections, and when need be, to adopt the 

 body to foreign proteins. The spontaneous recovery from 

 infectious disease, by which is meant merely that the 

 body by its own power overcomes the microbes and their 

 poisons, depends upon the setting into motion of the series 

 of operations through which immunity responses in fluids 

 and cells are insured, precisely as has been described in 

 the event of an artificial immunization. Hence in our 

 efforts at serum therapy we aim merely to aid "nature," 

 by introducing, as it were, into the beset body the finished 

 immunity products artificially produced in healthy ani- 

 mals ; and in protection by vaccination, success is assured 

 only to the extent to which the healthy body has been com- 

 pelled to prepare the specific immunity substances and to 

 hold them ready at hand to combat the entrance through 



