i8o THE DANGER OF FLIES 



features in the prevalence of infantile diarrhoea is that 

 it follows the rise and fall of the earth's temperature, 

 and not that of the air. In the same way the number 

 of house-flies does not reach its maximum with the 

 first burst of hot weather. The prevalence of these 

 insects follows rather than coincides with periods of 

 great heat. The flies, in fact, lag behind the air 

 temperature and persist for a time after the hot 

 weather has ceased. In other words, the meteoro- 

 logical conditions associated with an increase or a 

 diminution of the prevalence of diarrhoea exercise a 

 similar influence on the prevalence of flies. 



The transference of the Filaria bancrofti, whose 

 presence in the human body in the adult stage is 

 associated with various diseases of the lymphatics, 

 the most pronounced of which is the terrible ele- 

 phantiasis, is due to more than one species of gnat or 

 mosquito. It is true that no one has ever seen the 

 actual transference of the Filaria from the biting 

 organs of the Culex, Anopheles, Panoplites, or Stego- 

 myia into the human body, but the circumstantial 

 evidence is so strong that on it any jury would 

 convict. Noe and Grassi have demonstrated a similar 

 mode of infection for the Filaria immitis, which exists 

 in the adult stage in such incredible numbers in the 

 cavity of the right side of the heart of dogs, especially 

 in tropical and in sub-tropical countries, that it is 

 difficult to see how the circulation can be maintained 

 at all. It is therefore interesting to note that the 

 proboscis of our common house-fly frequently harbours 

 a larval nematode which has been described by 

 Carter* under the name of Habronema muscce ; and 

 again (if it be the same species) by Generalif under 

 the name Nematodum sp. (?), and again by Piana,} who 



* Ann. Nat. Hist., ser. 3, vii., p. 29. 



t Atti Soc. Modena, ser. 3, ii., Radiconte, p. 88. 



% Atti Mus. MilanOy xxxvi., 1896, p. 239. 



