INTERMEDIARY HOST OF FILARIA IMMITIS, LEIDY. 41 



PRELIMINARY NOTES on the INTERMEDIARY HOST 



of FILARIA IMMITIS, LEIDY. 



By Thomas L. Bancroft, m.b. Edin. 



[Read before the Royal Society of N. 8. Wales, June 5, 1901.'] 



Filaria immitis is a large worm-parasite of the dog, common 

 throughout the world, especially in the warmer parts ; it is from 

 five to ten inches in length, the males being much smaller than 

 the females ; it takes up its abode generally in the right ventricle 

 of the heart and in the pulmonary artery. These worms are very 

 prolific, producing large numbers of young, the so-called embryos; 

 the latter swim about in the blood ; a single minim of blood fre- 

 quently containing twenty or more of them, the number depending 

 of course on the number of fertile females in the dog; the embryo 

 is about -cjV inch in length by ^- 5 - -o inch in breadth. 



That distinguished scientist, the late Dr. Spencer Cobbold 

 taught us that an intermediary host was necessary to transmit 

 the parasite from dog to dog, and his opinion was accepted as 

 correct. 



Many workers in. various countries, more particularly Grassi, 

 Sonsino and J. Bancroft, endeavoured to discover the intermediary 

 host ; the dog-flea Pulex serraticeps was suspected, but no one 

 could trace the young filarise in its body after the blood containing 

 them was digested. The different dog lice and ticks were likewise 

 examined but with negative results. The writer has been 

 endeavouring for the past thirteen years to find the intermediary 

 host ; at first numerous examinations of the Pulex serraticeps 

 were made, afterwards of the common horse fly Stomoxys sp. ?; 

 Culex vigilax, Skuse, a day-flying mosquito ; the intestinal worm- 

 parasite of the dog the Anchylostoma or Dochmius trigonocephalus. 

 All these animals abstract together with blood the embryos, but 



