322 Lesions Produced by the Bite of the Black- fly 



$. The toxic agent is rendered inactive or destroyed by hydro- 

 chloric acid in a concentration of 0.25%. 



6. The toxic agent is most abundant in the region of the ana- 

 tomical structures connected with the biting and salivary apparatus 

 (head and thorax) . 



7. The toxic agent is not affected by a 0.5 % solution of sodium 

 bicarbonate. 



8. The toxic agent is not affected by exposure to dry heat at 

 100° C. for two hotus. 



9. The toxic agent is destroyed or rendered inactive in alkaline 

 solution by a typical hydrolytic ferment, pancreatin. 



10. Incomplete experimental evidence suggests that the activity 

 of the toxic agent may be heightened by a possible lytic action of 

 the blood serum of a sensitive individual, and that the sensitive serum 

 itself may contain the toxic agent in solution. 



These results, as far as they go (omitting No. 10), accord with 

 Langer's except on the point of alcoholic solubility and the effect 

 of acids. The actual nature of the toxic agent in the black-fly is 

 left a matter of speculation. 



The following working theories have suggested themselves to 

 the writer. First, the toxin may be, as Langer believes in the case 

 of the bee, an alkaloidal base, toxic as such, and neutralized after 

 injection by antibodies produced for the occasion by the body. In 

 such a case the view that a partial local fixation of the toxin occurs, 

 which prevents its immediate diffusion, is acceptable. Through 

 chemotactic action, special cells capable of breaking up the toxin 

 into harmless elements are attracted to the scene. Their function 

 may be, on the other hand, to neutralize directly, not by lysis. 

 This would explain the r61e of the eosinophiles in the black-fly lesion. 

 If their activities be essential to the destruction or neutralization 

 of the toxin, one would expect them to be most numerous where 

 there was least reaction. This wotild be at the site of a bite in an 

 immime individual. A point of special interest for fiirther investiga- 

 tion, wotald be the study of such a lesion. 



Second, it is conceivable that the injected saliva of the fly does 

 not contain an agent toxic as such. It is possible, that like many 

 foreign proteins, it only becomes toxic when broken down. The 

 completeness and rapidity of the breaking down depends on the 

 niunber of eosinophiles present. In such a case immunity should 

 again be marked by intense eosinophilia. 



