232 THE PRINCIPLES OF IMMUNOLOGY 



and Frank claim that the attacks may be intensified and prolonged 

 because of a concurrent acute or sub-acute bacterial infection, which 

 perhaps permits greater absorption of the pollen protein. The condition 

 may be so severe as to be called asthma, and in addition to respiratory 

 phenomena may show erythematous and urticarial eruptions. Similar 

 conditions are met with in certain individuals sensitive to the effluvia of 

 horses, rabbits and other animals. It is well known that the ingestion 

 of certain foods, such as egg albumin, shell fish, strawberries, may give 

 rise to serious intestinal disturbances and that these may occasionally be 

 associated with skin eruptions or respiratory disturbance. In sensitive 

 individuals contact of the skin with plants or animals, to the protein of 

 which the individual may be sensitive, leads not uncommonly to cutane- 

 ous eruptions. These, however, are not likely to be very severe or of 

 long duration. The inflammation of the skin in ivy or sumac poisoning 

 is not to be included in this group, because the irritant agent is prob- 

 ably not of protein nature, but rather an" acid-resin. Eczema and per- 

 haps certain other skin diseases may also be due to hypersusceptibility, 

 and it is found that this is exhibited rather toward food products than 

 toward other forms of protein. Furthermore, certain of these cases 

 of asthma, eczema, etc., may be due to bacterial proteins as well as 

 those of higher plants and of animals. 



The hypersusceptibility of the sort discussed in this section differs 

 from induced hypersusceptibility in two important respects. In the 

 first place, the degree of sensitiveness is extreme. This may be illus- 

 trated by the case reported by Boughton, quoted above, in which one 

 minim of horse serum produced death. It is further illustrated by the 

 fact that hay fever, asthma and other similar conditions are induced 

 by what must necessarily be an extremely small amount of protein 

 in the atmosphere. In the second place, the sensitization is not limited 

 strictly to a single protein. Longcope classifies these individuals roughly 

 as those " who react to the sera of animals ; those who react to eggs, 

 or the sera of fowls ; those who react to the extracts of shell fish and 

 those who react to the protein of plants." Within each group the 

 individual may be sensitive to the protein of several species. As has 

 been pointed out by Walker, those who react to bacteria frequently 

 react to several varieties of organisms. Furthermore, individuals may 

 occasionally show reactions to two or three of the large groups indicated 

 by Longcope. Of further interest in regard to specificity is the fact 

 that apparently within a given species, proteins of somewhat different 

 origin may not produce identical reactions. For example, skin reac- 

 tions may demonstrate sensitiveness to horse dandruff and not to horse 

 serum. Desensitization may be produced by careful and prolonged 

 vaccination, but as in experimental animals the desensitized state does 

 not persist for a very extended period, it may be necessary to repeat 

 the vaccinations every six months, every year, or at such other periods 

 as the individual case requires. The possibility of passive sensitization 

 in natural hypersusceptibility is illustrated by a case reported by 

 Ramirez. A man who had never shown any hypersensitiveness to proteins 



