272 OTHER INTESTINAL ROUNDWORMS 



of chloroform against hookworms may be due to the fact that 

 hookworms are blood-suckers and that the chloroform rapidly 

 absorbed by the blood is ingested by the hookworms in amounts 

 sufficient to cause stupefaction or death. 



The presence of intestinal worms of most species can be de- 

 termined by the finding of the eggs in the faeces, and in most castft 

 the eggs are characteristic enough to make a determination of 

 the species fairly easy. It often facilitates the search for para- 

 site eggs to concentrate them in the following manner: Mix a 

 portion of the faeces the size of a walnut with 60 cc. of distilled 

 water, strain through several thicknesses of wide-mesh surgical 

 gauze and centrifuge at high speed for about ten seconds. Pour 

 off most of the liquid, add more water, shake thoroughly and 

 centrifuge again. The material thrown to the bottom of the 

 tube contains the eggs, which can readily be found under a micro- 

 scope. A bit of the centrifuged material is placed on a slide with 

 a little distilled water. In two or three minutes the eggs will 

 settle on the slide, and the excess liquid can be poured off. The 

 eggs of parasitic worms vary in size, shape, color, surface mark- 

 ings and state of development. Most eggs are colored yellow 

 or brown from bile in the faeces but the eggs of the hookworms, 

 Strongyloides, and a few others remain clear and colorless. The 

 characteristics of the eggs of the commoner parasitic worms are 

 shown in a comparative way in Fig. 61, p. 205. In the case of a 

 few intestinal nematodes eggs do not appear in the faeces. In 

 the pinworms, for instance, the adult female containing the eggs 

 usually passes out entire, whereas in Strongyloides the eggs hatch 

 before leaving the host. 



Preventive measures against practically all of the true nema- 

 tode parasites of the intestine consist mainly in proper sanitation, 

 a discussion of which will be found on p. 265. It is possible that 

 some of the intestinal nematodes may occasionally, at least, 

 utilize an intermediate host of some kind, but even if this were 

 true sanitary disposal of human faeces would, as said before, be 

 sufficient to exterminate such parasites as are peculiar to man. 

 The nematodes which occur in other animals as well as man have 

 to be guarded against by other means also. The spiny-headed 

 worms, which are transmitted in the bodies of insects which 

 serve as intermediate hosts, are, of course, subject to quite dif- 

 ferent prophylactic measures. 



