STRONG YLOIDES 281 



the body, visible through the delicate body wall. The eggs, 

 which are deposited deep in the intestinal coat, normally hatch 

 before leaving the digestive tract of the host and grow con- 

 siderably, so that when the faeces of an infected person are ex- 

 amined microscopically the active writhing larvae (Fig. 113B), 

 2.50 yu (t^xt of an inch) in length, can be seen darting about in 

 snakelike fashion. Further development of the larvae takes 

 place in water of fairly high temperature, such as would be found 

 under the burning rays of a tropical sun. Under such conditions 

 the larvae attain a sexually mature form, male and female (Fig. 

 113C and D), in which they are quite different from their parents. 

 They now copulate, and the females lay 30 or. 40 eggs, all within 

 two days. This second generation of eggs hatch into tiny free- 

 living larvae (Fig. 113E) resembling the parents, but after their 

 first moult they lose the parental characteristics and become 

 like their grandparents (Fig. 113F). After having reached this 

 stage, they soon die unless they gain entrance to the digestive 

 tract of a human being again. An unusual phenomenon is 

 shown by these worms in that the life cycle, under less favorable 

 conditions, can be abridged, and the alternation of generations 

 eliminated. If, for instance, the larvae in the faeces be exposed 

 to the cooler water of a temperate country, they do not be- 

 come sexually mature and reproduce, but transform diretly 

 into the parasitic type and reinfect without further repro- 

 duction. 



The method of infection is similar to that of the hookworms. 

 While the larvae may occasionally gain entrance to their host 

 with polluted water or food, they are able to bore through the 

 skin as do the hookworm larvae, and it is probable that this is 

 the more usual method. 



As a rule Strongyloides does not cause very serious ill effects 

 from its pursuit of life and happiness in the intestine. Nearly 

 all cases of diarrhea and dysentery, in which the strongyloids 

 were formerly supposed to be the chief agent, can now be ascribed 

 to some other cause, the strongyloids being more or less innocent 

 bystanders. Barlow, however, reports that in 23 cases in 

 Honduras, five of them uncomphcated, such symptoms as in- 

 termittent diarrhea without blood or mucus in the stools, colic 

 and certain nervous symptoms were in evidence. In many cases 

 where a diseased condition of the intestine is brought about by 



