ANAPHYLAXIS AND HYPERSUSCEPTIBILITV 177 



the first. Evidently there may be an inborn or a developed sen- 

 sitiveness in man to serum injection. 



Theobald Smith Phenomenon. Theobald Smith made the 

 observation that when guinea-pigs are injected with horse serum, 

 and a second injection is given after the space of ten days or more, 

 the pig will show signs of hypersensitiveness, and if a sufficient 

 quantity, 5 or 6 c.c., is injected intraperitoneally, death will result 

 in a few minutes. The first injection serves to sensitize against 

 the second. This phenomenon in the guinea-pig is so striking that 

 it has been used by many investigators in a study of the reaction. 

 The general phenomenon was given the name of anaphylaxis. 

 This will be discussed, and its utilization in diagnosis and in ex- 

 planation of certain hitherto obscure body reactions reviewed. 



Antibodies in Anaphylaxis. Many of the factors determining 

 anaphyla'xis are at present imperfectly understood. Enough is 

 known, however, to enable us* to account for many hitherto 

 obscure body reactions. Various species of animals show different 

 types of anaphylactic reaction, but the differences are, according 

 to Anderson and Frost, mainly quantitative the nature is the 

 same, although the manifestations are different. 



Sensibilisinogen. The antigen used in developing anaphylaxis 

 is known as the sensibilisinogen. In experimental work upon 

 guinea-pigs practically all proteins have been found to sensitize, 

 among them, blood-serum of many animals, egg-white, milk, 

 extracts from body organs and cells, plant proteins, bacterial 

 proteins, yeast proteins, and even some of the peptones formed 

 by the peptic digestion of proteins. Experiments have shown that 

 the sensibilisinogen is thermostabile; in many cases it will still 

 sensitize after heating to a temperature above boiling. 



Allergin. The injection of the specific protein or sensibili- 

 sinogen has been shown to cause the production in the blood of the 

 guinea-pig of an antibody which has been variously termed 

 allergin, sensibilisin, immune body, and anaphylactin. Either 

 of the first two names is to be preferred to the others. That 

 some kind of an antibody is formed may be shown by injecting 

 the serum of a sensitized animal into a normal animal, which will 

 then show the anaphylactic reaction when injected with the proper 

 sensibilisinogen. Evidently a sensitizing substance (the allergin) 

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