282 TiMEHRI. 



Guiana affords numerous typical examples. Of these it 

 will be sufficient for my purpose to briefly describe the 

 following: — Ascaris lumbricoides, Anchylostomum duo- 

 denale, Trichocephalus dispar, Filaria medinensis, and 

 Filaria sanguinis hominis ; the descriptions in most cases 

 being taken from AlTKEN'S Science and Pra6lice of 

 Medicine. 



The Ascaris lumbricoides, or round worm, is the most 

 common of human entozoa. It is much more common in 

 children and adults than in old people. And it is very 

 much more common in the children and adults of British 

 Guiana (and probably other tropical countries) than in 

 more temperate climates. Very few post-mortem 

 examinations in British Guiana fail to reveal the presence 

 of one or more of these extremely loathsome looking 

 animals. In some cases they are so numerous as abso- 

 lutely to obstru6l the intestines. These Ascarides in- 

 habit chiefly the small intestines, but may pass up into 

 the gall-du6ls, the stomach, the oesophagus, the nostrils, 

 mouth or frontal sinuses. They are extremely fertile, 

 and it has been calculated that there are sixty-four 

 millions of ova in every mature female Ascaris ! 



"What becomes of all these ova ? Being discharged by 

 millions, many of them, in large cities, are carried into 

 streams of water." There they may become food for 

 numerous inhabitants of the water. After a certain length 

 of time under favourable conditions each ovum contains 

 a living embryo ; but the embryos may remain in this im- 

 prisoned or encysted state for many months or even 

 years together, and it is not until the shell of the egg is 

 broken through that the embryo can escape. After 

 escape from the shell the embryo is capable of living 



