Chapter J 



Idiosyncrasy and Anaphylaxis and Their 

 Relation to Organismal Differentials 



The term "idiosyncrasy" implies a peculiar state of hypersensitiveness 

 to a certain substance, which may characterize an individual and 

 distinguish him from others. In an analysis of individuality a discus- 

 sion of such a condition should therefore be of interest. While usually only a 

 small minority of persons are affected by an idiosyncrasy towards a substance, 

 after all, the frequency with which various substances are responsible for 

 such a condition differs greatly. There exists, for instance, a potential 

 idiosyncrasy to the injection of foreign serum, especially horse serum, causing 

 serum disease among a considerable number of individuals; likewise, the 

 tendency to become hypersensitive to extracts of ascaris is almost universal 

 among those infested with this parasitic worm. On the other hand, a hyper- 

 sensitiveness to chicken egg is not frequent, while to less complex chemical 

 substances, such as antipyrin, it is quite rare. 



However, idiosyncrasy has an additional meaning. It signifies an individual 

 state, which is not explained solely by the specific character of the substance 

 eliciting it, but which, to a large extent, is due to the characteristics of the 

 individual affected. Certain of the principal mechanisms involved are now 

 understood, at least in their general outline, but others are as yet unexplained. 



As a rule, hypersensitiveness to most of the substances with which we 

 have to deal in indiosyncrasy is localized in definite tissues, without otherwise 

 affecting seriously vital functions of the organism ; but in certain cases central 

 mechanisms, on the integrity of which all other functions depend, may be 

 involved and then an idiosyncrasy may cause rapid death. Such an effect may 

 be observed, for instance, in the so-called serum disease, where in some indi- 

 viduals even a first injection of a heterogenous serum, usually horse serum, 

 may call forth very acute general reactions not unlike those of anaphylactic 

 shock. The organs most commonly affected in idiosyncrasy are the respiratory 

 system, especially the nasal mucosa in hay fever and the bronchi in asthma, 

 the gastro-intestinal tract in food hypersensitiveness, the skin in many condi- 

 tions in which certain substances act primarily on this organ ; and the skin 

 may show reactions also in cases in which primarily other organ-systems are 

 involved. 



While thus one idiosyncratic individual may differ from another one as 

 to the factor which causes the hypersensitiveness and elicits the abnormal 

 reactions, the modes of reaction and the organ-systems which are hyper- 

 sensitive are remarkably similar in different individuals. In general, it seems 

 that the tissue on which a given injurious substance acts primarily, is the one 

 which becomes primarily hypersensitive to that substance, although subse- 



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