CONTROL OF BLACKFL1ES 483 



was so intense that I was in agony all night and could not sleep. 

 Accompanying this there was a feeling of general " ennui " 

 and despondence with some fever, due, no doubt, to the action 

 of the poison injected by the numerous insects. Subsequent 

 attacks by the flies, though always far from pleasant, were not 

 so severe in their effects, a certain amount of immunity appar- 

 ently having been built up. On account of the slow develop- 

 ment of the symptoms it was my belief that possibly they were 

 due to the injection of a living organism. Stokes, however, 

 has shown that the effects of blackfly bites, essentially as de- 

 scribed above, can be reproduced by the injection of material 

 from preserved flies. An interesting suggestion is made by 

 Stokes that possibly the first bites of the flies sensitize the body 

 to the particular poison injected so that it reacts rather violently 

 to subsequent injections of it. This phenomenon, which is 

 known to occur in connection with many poisonous substances, 

 is a form of anaphylaxis (see p. 24). Possibly the rashes pro- 

 duced by mites, lice, etc., may also be due to such a reaction. 



As yet blackflies are not known to be the carriers of any dis- 

 eases. A theory was rampant a few years ago that pellagra was 

 due to a protozoan transmitted by blackflies, but it is now gen- 

 erally held that this disease is due to an imperfect diet, or rather 

 to lack of the necessary assortment of substances in the diet, 

 and so is in no way connected with blackflies or other insects. 



Control. Since blackflies breed in running water the methods 

 to be employed in their extermination are quite different from 

 those ordinarily used in the extermination of mosquitoes. One 

 of the measures most widely used is the treatment of breeding 

 streams with phinotas oil, a poisonous oil which forms an emul- 

 sion in the water and slowly soaks through it. In concentrations 

 sufficient to destroy the larvae, however, this oil is also destruc- 

 tive to fish. Often the breeding grounds of blackflies may be 

 locally destroyed or reduced by damming the stream at inter- 

 vals, leaving falls between, or in the case of small brooks by the 

 construction of underground channels or of a drain-pipe line. 

 The clearing away of roots and fallen logs from streams is often 

 of value, in that it removes surfaces on which the eggs are laid, 

 and obliterates the numerous small falls which are ideal for the 

 larvae. In larger streams the cultivation of fishes, such as trout, 

 young bass, darters, etc., greatly reduces the number of black- 



