CHAPTER 7 

 THE ANTIGEN-ANTIBODY REACTIONS 



The problems of infection and resistance — the nature of the mechanisms which 

 determine the course of events when a potentially pathogenic parasite gains access 

 to an animal host — will be discussed in later chapters. 



Very early in the development of this field of research investigators began to 

 study the reactions which occur when blood, blood serum, or other body fluids 

 are allowed to react in the test-tube with bacteria, or with bacterial products. 

 Almost from the first, the study of these reactions was pursued by many workers 

 without particular reference to the role, if any, which they played in the combat 

 between parasite and host ; and it soon became clear that they provided a new 

 technique, which could be ajiplied to a variety of biological problems quite apart 

 from the study of disease. 



The development of our knowledge of the various reactions which may occur 

 when the blood or serum of a given animal is mixed with various bacteria, bacterial 

 products, foreign cells, or foreign proteins, may be briefly summarized as follows. 



In 1888 Nuttall demonstrated that the defibrinated blood of certain animals 

 had the power of killing certain bacteria. Buchner (1889o, b, c) showed that this 

 bactericidal power was possessed by the cell-free serum, and that it was lost when 

 the serum was heated to 55° C. for 1 hour. 



In 1890 von Behring and Kitasato showed that the serum of animals which had 

 received repeated injections of non-lethal doses of tetanus toxin, or of diphtheria 

 toxin, had acquired the property of specifically neutralizing these toxins, and thus 

 preventing their poisonous effect. 



Between 1893 and 1895 Pfeifier (see also Pfeiffer and Issaeff 1894) recorded the 

 occurrence of bacteriolysis, or granular degeneration followed by partial dissolution, 

 in cholera vibrios and some other bacteria, when these were introduced into the 

 peritoneal cavity of guinea-pigs which had previously received inoculations of killed 

 cultures of the particular bacteria in question. They showed, also, that the 

 substances which determined this bacteriolysis were present in the blood serum, 

 and in other body fluids. 



In 1895 Bordet published his classical paper on the properties of the sera of 

 immunized animals. We may note here that, although the idea of increased 

 resistance to infection was implicit in the early conception of the process of im- 

 munization, this term soon came to possess a wider meaning. Any animal, into 

 whose tissues has been introduced any antigenic foreign substance, dead or living, 

 and whose serum has, in consequence, gained the property of reacting in some way 

 with that particular substance, is spoken of as having been immunized against it ; 

 and such a serum is referred to as an immune serum or an antiserum. Bordet, 

 extending the observations of Buchner, showed that two different substances are 



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