HYPERSUSCEPTIBILITY 209 



immunity. In man natural hypersusceptibilities are believed to be 

 manifested upon the introduction of the special proteins or similar sub- 

 stances into the respiratory tract, the alimentary canal, into the skin and 

 by injection into the tissues, body spaces or circulation. Man may 

 exhibit respiratory symptoms in the presence of vegetable effluvia, as in 

 " hay fever," " rose fever," and of the effluvia of certain animals, such 

 as the horse and guinea-pig. In individuals thus susceptible, local or 

 general reactions may occur following inoculation with the specific 

 animal or vegetable protein. The ingestion of animal proteins, such as 

 egg, or vegetable proteins, such as strawberry, may produce severe 

 gastro-intestinal disturbances sometimes accompanied by general symp- 

 toms. In certain cases this hypersusceptibility may have been acquired 

 by previous sensitization, but in the greater number no such explanation 

 is to be offered. In babies susceptible to egg-white there is no prob- 

 ability that preliminary direct sensitization occurs, but it is possible 

 that the tendency to hypersusceptibility may have been inherited. The 

 instances mentioned are examples of individual hypersusceptibility. 

 Although less clear cut there are also evidences of species hypersuscepti- 

 bility, as, for example, the fact that ox serum is distinctly toxic for 

 guinea-pigs and much less so for man. The acquired forms of 

 hypersusceptibility will be considered under the general discussion 

 of anaphylaxis. 



Anaphylaxis. Following the introduction of the serum treatment 

 of disease, disturbing elements appeared, the most striking of which 

 were the frequent production of " serum rashes " and the reports of 

 occasional severe constitutional reactions and even sudden death. Von 

 Pirquet and Schick pointed out on the basis of a clinical investigation 

 in connection with the serum treatment of diphtheria and scarlatina, 

 that in from seven to twelve days following a single injection of serum 

 or several injections on successive days, a so-called " serum disease " 

 appears. This is characterized by macular or maculo-papular eruptions 

 of urticarial type, malaise, fever and other symptoms. After this period 

 a subsequent injection of the same protein leads to the appearance of 

 similar symptoms and signs usually within twenty-four hours. After 

 the lapse of months or years the reaction may be delayed and fail to 

 appear for several days, but is only rarely as late as that following the 

 primary injection. In other words, the patients appeared to have been 

 sensitized by the primary injection. Not being able to define exactly 

 the nature of this condition, the name allergy was suggested, indicating 

 an " altered state " of the animal body. The usage of the term at the 

 present time is confusing and definitions vary ; we, therefore, prefer not 

 to employ it. 



Experimentally similar phenomena had been noted in the course of 

 other studies as far back as Magendie in 1839, but it remained for 

 Richet and Portier in 1902 to point out the fact that an animal may be 

 rendered hypersusceptible to a poison, by the previous injection of a 

 small dose. They used actino-congestine, a toxic , protein extracted 

 from the tentacles of actinia. Because the phenomenon indicates a 

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