206 president's addeess. 



rilarise, — an estimate probably not erring on the side of excess. 

 "Within its geographical range the parasite attacks very largo 

 numbers of persons, but in most cases without producing serious 

 symptoms ; in others, however, it seems to be the exciting cause 

 of several diseases, such as elephantiasis, chyluria, etc. In 

 Bahia it has been stated that 8-^ per cent, of the population are 

 affected by it. To the biologist the chief interest of the animal 

 is centred — as with so many other parasites — in its life-history, 

 and it is to Dr. Manson that we owe most of our knowledge of 

 the subject. One very remarkable fact is that the creature 

 seems to forsake the superficial blood vessels during the day, 

 and can rarely be seen until after seven o'clock in the evening. 

 Dr. Manson was thus led to suppose that if the worm passed any 

 part of its life in the body of an "intermediate" host, that host 

 would probably be some night-feeding, blood-sucking creature 

 like the mosquito. He accordingly got a Chinamen, known to 

 be affected with Filariae, to shut himself up with some mosquitos 

 and submit to their blood-thirsty attentions. On examination 

 of the insects afterwards their blood was found to be swarming 

 with Filarise. It seems probable that some of these may be 

 digested by the mosquito, but that others find their way from 

 the stomach into the surrounding tissues, and there pass into a 

 higher stage of development. The mosquito betakes itself to 

 some pond or reservoir, as the habit of its tribe is, there deposits 

 its eggs, and speedily dies, decomposes, and of course liberates 

 the embryo Filariae, which doubtless find frequent access to the 

 human organism in drinking-water. That Europeans are less 

 frequently affected than natives must be owing to the greater 

 care taken by them as to filtration of water. Such precautions 

 are unknown to the native races, and it seems wonderful, not 

 that so many should be affected but that any should entirely 

 escape. 



Another round-worm which, for us in England, has a more 

 personal interest is Trichina spiralis. Tliis creature passes its 

 encysted existence, often in immense numbers, in the muscles 

 of the pig, though its true host is said to be the rat. Eor its 

 further development the flesh of the pig must be eaten by some 



