42 



THOMAS L. BANCROFT. 



the latter appear not to enter upon a metamorphosis, and after 

 several days can no longer be traced ■ it is thought that they are 

 digested. 



It occurred to me as possible, that a metamorphosis was not 

 necessary, but merely that the embryo should go through a cold 

 stage for a few days in the body of an insect, after which should 

 it gain entrance into a dog it would start upon its final develop- 

 ment. To test this hypothesis, a feeding experiment on a puppy 

 was made. The dog swallowed at various times during a month 

 one hundred and ten Stomoxys flies gorged with filariated blood ; 

 in each fly there were about fifty embryos. Every month after- 

 wards the dog's blood was submitted to microscopic examination ; 

 at the expiration of eight months, two embryos were detected on 

 a slide containing two minims of blood ; a month later there were 

 ten embryos in the same quantity of blood; the number however, 

 after this date did not increase; the dog was killed and search 

 made for the mature worms, three only were found in the heart, 

 two females and a male. Now were the hypothesis correct we 

 should expect to have found hundreds of mature worms. This 

 dog must have been infected whilst with its mother; it was three 

 or four months old when I got it, and whilst under observation it 

 was kept apart from other dogs. The experiment not only 

 disproved the hypothesis, but served another purpose, viz., the 

 time taken by the young filaria to arrive at sexual maturity was 

 ascertained to be not less than seven months and not more than 

 a year. 



In the British Medical Journal Nov. 3, 1900, p. 1306, there is 

 a paper by B. Grassi and G. Noe of Rome, entitled "The propa- 

 gation of the filarise of the blood exclusively by means of the 

 puncture of peculiar mosquitos." In this paper, mention is made 

 that Grassi, whilst engaged experimenting with the malarial 

 mosquito, the Anopheles maculipennis, Meigen, Syn. A. claviger, 

 Fab., had observed filarise in them, which he traced to be develop- 

 mental forms of Filaria immitis. To Grassi therefore is due the 

 credit of having discovered the intermediary host. 



