48 GUIDE TO THE STUDY 



Permanent mounts of the various eggs used in this practicum may 

 be prepared by Looss' method (p. 109) and sealed with Noyer's 

 cement. 



METHOD OF FECES EXAMINATION 

 The determination of parasitism in the living host can rarel> 

 be made on the basis of clinical symptoms. It requires usually 

 the microscopic examination of the various excreta, of the blood, 

 and even of bits of living tissue. A large number of endoparasites 

 inhabit the alimentary canal or glands, such as the liver, of 

 their host and discharge their eggs or larvae or segments in 

 the feces. To some extent in man and commonly in animals, 

 eggs of lung parasites are likewise swallowed and pass through 

 the intestine. Their presence in the living host is then revealed 

 by the examination of the feces. This examination may be 

 both macroscopic and microscopic. The parasites concerned 

 may be protozoal, helminth, or arthropod. In this practicum we 

 shall restrict our attention largely to the helminths, and par- 

 ticularly to the recognition of the eggs of these forms. 



Macroscopic examination of normal stools is very superficial 

 and to be trusted only when it is positive. More definite infor- 

 mation can be obtained by giving the patient a vermifuge and 

 examining all of the stools for a period of at least 48 hours. The 

 fecal material is broken up in a large quantity of water in a 

 flask and as rapidly as it settles the supernatent fluid is decanted ; 

 or the stool is washed repeatedly through a fine-meshed sieve. 

 The sediment is poured into a tray and examined for segments 

 of tapeworm, small nematodes, and flukes. A black photo- 

 graphic tray is useful for this examination. 



Microscopic Examination. — The simplest method of micro- 

 scopic examination is to remove several samples of the stool, 

 about the size of a pinhead, emulsify on a slide in clean water, 

 and cover with an 18-mm. square cover glass. If the stool is 

 quite fluid, it may not need dilution. Care should be taken not 

 to have the preparation too opaque, for eggs and cysts may be 

 overlooked. On the other hand, if it is too thin, time is wasted 

 in search. A good rule is to have it thin enough for ordinary 

 print to be read through the preparation. 



Simple Sedimentation.— The search for microscopic evidences 

 of parasitism may be considerably lightened by thorough and 

 repeated sedimentation of stool samples. Finally small quan- 

 tities of the sediment are mounted for examination. 



