252 



NATURAL BISTORT. 



animal, it cannot suffer from the painf ul and dangerous disease which is set up by the young worms, as 

 they grow to a certain life-stage, in the muscles. And, moreover, the only manner in which the 

 Trichinae can get into the digestive system is by their being swallowed alive, with pieces of improperly 

 cooked muscle in which they are encysted. Men are infected by eating badly-cooked pork, the pig 

 happening to suffer from the presence of the worm in its muscles. Leuckart stated that, as a rule, 

 " swine obtain their Trichinae from rats, to which latter we also, as natural bearers, have to convey 

 them." Cobbold has shown the stupendous number of Trichinae an animal may have within its- 

 muscles at one time, and he proved that 80,000 were in an ounce of pig's flesh belonging to an animal 

 part of which had been unfortunately eaten, and had produced an epidemic. 



The " Whip Worm "* has a long filiform neck two-thirds of the length of the whole body, and the 

 surface of the skin has, on one side, a longitudinal band of minute wart-like papilla?. The Whip 



Worms infest the caecum and the upper part of the great intestine 

 or colon, and many thousands have been found in the human 

 subject. 



Cobbold describes the wonderful story of the life of one of the 

 species t of the genus Filaria, and notices that the body of it is 

 like a hair, uniform in thickness, and that the head has a simple 

 circular mouth without papilla?. The neck is narrow and about 

 one-third of the width of the body, and the tail of the female is 

 single, bluntly pointed. They are three inches and a half long and 

 g*oth of an inch broad. The eggs are about yoVoth of an inch 

 in length, and the embryos derived from them are ^^th to ^i^th 

 of an inch in length. 



The embryos were first discovered in human, urine, and 

 Cobbold got eggs and embryos from a man from Natal whilst 

 searching for the parasite called Bilharzia. In 1872 Dr. Lewis 

 found these microscopic worms in the human blood, described 

 them, and gave the species the name of Filaria sanguinis homini. 

 In 1876 Dr. Bancroft found the eggs in the blood, and discovered, 

 subsequently, the mature form already noticed, and observed that 

 immense numbers of minute living ones are passed from its 

 body. 



Dr. Manson, in 1878, found the immature or embryonic 

 Filaria in the stomach of Mosquitoes which had sucked the blood of 

 man, and probably also that of birds. The female Mosquitoes, after 

 gorging themselves with blood, repair to stagnant water to deposit their eggs, and during the four or 

 five days thus occupied the Filarise within undergo remarkable changes. Subsequently they become 

 more fully developed, and escape from the Mosquitoes into the water, and may be drunk by man. 



The largest known Nematoid Worm is called Emtrongylus gigas, the male measuring a foot and 

 the female more than three feet in length. The breadth of this huge worm is half an inch at the 

 thickest part. This worm is known to occur in a great variety of animals. 



The Guinea WormJ is a Nematoid measuring from one to six feet in length, and having the 

 thickness of one-tenth of an inch. The body is cylindrical, and has a pointed tail and a convex head,, 

 with a central mouth surrounded with papilla?. The body of the female encloses a prodigious number 

 of hatched embryos when she is mature, and they may have the opportunity of escaping from their 

 human host from the sores produced by the adult. The embryos escape into water and become 

 parasitic in the small Crustacea of the genus Cyclops, and undergo a change of skin and subsequent 

 growth. This condition of larval development lasts about five weeks, and when the larvae become 

 perfect they may be accidentally drunk with the Cyclops by men and animals. 



The Thread Worm, which is so frequently a parasite of children, also affects old people. The 

 male worm, according to Cobbold, measures one-sixth of an inch, and the female from one-third to one- 



F1LARIA BANCROFTII. (After Colibold.) 



A, female (nat. sizei ; B, head and neck ; c. tail : D, 

 free embryo ; K, egg with embryo ; r, egg with 

 mulberry cleavage of yolk. 



Trichocephalus dispar. 



J Dracunculus medinensis. (Cobbold.) 



+ Filaria bancroftii. 

 Oxyuris vermicularis. 



