president's address. 205 



awaits the chance of further development in the alimentary 

 track of some unfortunate man : should it fail to find its way 

 thither it ultimately dies, undergoing a process of calcareous 

 degeneration. But if it should, in the foi'm of insufficiently 

 cooked pork or bacon, be taken into the human stomach it then 

 enters upon its final metamorphosis; the cyst is detached and 

 the head begins to develop from behind an almost interminable 

 series of egg-producing segments or " proglottides," and so its 

 cycle of existence is completed. The prophylactic, in the case 

 of all Taeniae, is to have meat thoroughly well cooked throughout 

 and thus to destroy whatever encysted scolices it may contain. 

 Sometimes, however, man becomes, not the final but the inter- 

 mediate host, as in the case of Tania echinococcus—a parasite 

 which in its mature form infests the dog, but in its cystic condi- 

 tion causes in man the very serious disease known as " hydatids," 

 — a complaint not, happily, very common in England, but much 

 more so in Iceland and other counti'ies where dogs are allowed 

 to feed unchecked upon uncooked offal, and so to perpetuate the 

 existence of the parasite. 



Another extremely interesting Entozoon, belonging to the 

 group Nematelmia or round-worms, is a small species called 

 Filaria sanguinis hominis,^' which is found in very large num- 

 bers in the blood of the human subject, but is restricted in its 

 geographical distribution to the tropical and subtropical regions 

 of both hemispheres. The female of this worm attains a length 

 of three inches and a half, is very slender and hair-like, and is 

 formed singly in some vessel of the lymphatic system, where it 

 seems to lie quiescent, and produces viviparously very large 

 numbers of young Filarise, which find their way readily into the 

 blood vessels. The history of this creature has been carefully 

 investigated by Dr. Patrick Manson, of Amoy, China ; by Dr. 

 T. E,. Lewis in India, by Dr. J. Silva Lima in Brazil, as well as 

 by other observers. The animal as met with in the human 

 blood system is immature, and measures on an average about 

 one twenty-fifth of an inch in length. Dr. Lewis calculated that 

 in one of his cases there existed in the blood 140,000 of these 



* Filaria Bancrofti, Cobbold. 



