324 Lesions Produced by the Bite of the Black-fly 



Third, lytic agents in the blood serum may play the chief r61e 

 in the liberation of the toxic agent from its non-toxic combination. 

 An immune individual would then be one whose immunity was not 

 the positive one of antibody formation, but the negative immunity 

 of failure to metabolize. An immune lesion in such a case might 

 be conceived as presenting no eosinophilia, since no toxin is liberated. 

 If the liberation of the toxin is dependent upon lytic agents present 

 in the serum rather than in any cellular elements, a rational explana- 

 tion would be available for the apparent results (subject to con- 

 firmation) of the experiment with sensitive and immune sera. In 

 this experiment it will be recalled that the sensitive serum seemed to 

 bring out the toxicity of the ground flies, and the serum itself seemed 

 even to contain some of the dissolved or liberated toxin. The 

 slowness with which a lesion develops in the case of the black-fly 

 bite supports the view of the initial lack of toxicity of the injected 

 material. The entire absence of early subjective symptoms, such 

 as pain, burning, etc., is further evidence for this view. It would 

 appear as if no reaction occurred until lysis of an originally non- 

 toxic substance had begun. Regarding the toxin itself as the chemo- 

 tactic agent which attracts eosinophiles, its liberation in the lytic 

 process and diffusion through the blood stream attracts the cells 

 in question to the point at which it is being liberated. Arriving 

 upon the scene, these cells assist in its neutralization. 



The last view presented is the one to which the author inclines 

 as the one which most adequately explains the phenomena. 



A fourth view is that the initial injection of a foreign protein by 

 the fly (i.e., with the first bite) sensitizes the body to that protein. 

 Its subsequent injection at any point in the skin gives rise to a 

 local expression of systematic sensitization. Such local sensitization 

 reactions have been described by Arthus and Breton, by Ham- 

 burger and Pollack and by Gowie. The description of such a lesion 

 given by the first named authors, in the rabbit, however, does not 

 suggest, histopathologically at least, a strong resemblance to that 

 of the black-fly. Such an explanation of many insect urticarise 

 deserves further investigation, however, and may align them under 

 cutaneous expressions of anaphylaxis to a foreign protein injected 

 by the insect. Depending on the chemical nature of the protein 

 injected, a specific chemotactic reaction like eosinophilia may or 

 may not occur. Viewed in this light the development of immunity 

 to insect bites assumes a place in the larger problem of anaphylaxis. 



