BEARING HELMINTHES FEEDING EXPERIMENTS 119 



of Strongyloides stercoralis l (Bavay), which inhabits the intestine of 

 man. In the form found in Southern Europe, which is occasionally 

 imported into this country, the free-living generation is usually absent. 

 This is to say, the young worms of the parasitic generation do not 

 attain sexual maturity and do not multiply after leaving their host. 

 When in the open they transform themselves into larvae, whose 

 further development is dependent upon their importation into man. 2 



Looss 3 describes a method of isolating Nematode larvae, which is 

 very useful in the case of worms reared in faeces. He carried out the 

 method with Ankylostoma, but it may be employed for other parasitic 

 larvae. The faeces are first mixed with bone-black and then allowed 

 to stand, the mixture being occasionally stirred. The period of 

 development depends upon external temperature. With a high 

 reading of the thermometer, such as summer temperature in Egypt, 

 the surface of the culture will be covered with newly hatched larvae 

 in twenty-four hours. The culture is then exposed to the air until 

 the surface is covered with a thin, but firm, crust. If the vessels are 

 now filled up with clean water and allowed to stand for ten to twenty 

 minutes, the larvae will appear in large numbers in the water, and may 

 be poured off with it. The culture should be re-dried, and the process 

 repeated, until the larvae cease to appear in the water. To insure 

 absolute isolation, the water which has been poured off the culture, 

 and which will contain fine particles of faecal matter, should be filtered. 

 The water which first runs through the filter will be discoloured, and 

 should be thrown away as soon as the water begins to run clear. The 

 clear liquid will be found to contain larvae which have bored their 

 way through the filter paper, and these will appear in increasing 

 numbers. They will be found most abundantly, however, if the 

 empty filter is allowed to stand in the funnel for about twelve 

 hours, and clean water is again passed through it. This process 

 should be repeated until larvae cease to appear in the filtered fluid. 

 This method has also been found useful in isolating the larvae of 

 S. stercoralis* and should be applicable to many other species. 



The water containing larvae may be used to infect animals of 

 suitable species, and the details of the experiment will vary according 

 to the nature and habits of the Helminthes used. Those which 

 develop directly in a definite host (many Nematodes) will require a 



1 The Strongyloides of man should be examined with the greatest caution, as 

 infection with free larvae is possible, not only by way of the mouth, but by way of 

 the skin. This applies also to Ankylostoma duodenale. 



2 See Braun-Seifert's " Parasitenwerk," 4th ed., Wiirz., 1908, p. 288. 



3 Looss, Centralb. f. BaJct., Paras, und Inf., part 1, vol. xxi, 1897, p. 914. 



4 Braun, ibid., part 1, vol. xxvi, 1890, p. 614. 



