OBJECTIONS TO CERTAIN METHODS. 31 



with low-power lenses. As the determination of nematode genera 

 and species is in general more difficult from the embryos than from 

 the eggs, the usefulness of the culture method is limited. 



Emerson (1910) uses the following method in searching for 

 Strongyloides intestinalix : 



The stool should be placed in a dish, a small depression made on its surface, 

 this filled with water, and the stool left in a thermostat overnight. If embryos 

 are present, they are easily found * * * actively swimming in this water. 



Culture methods have been used by Ransom (190Gi) in studying 

 Hcemonchus contortus in sheep feces. Dr. Garrison tells me that he 

 has seen the culture method used successfully in Arnn r work in exam- 

 ining a company for hookworm infection. 



It is evident that such methods are suitable only for special pur- 

 poses and not for general work. 



OBJECTIONS TO CEETAIN METHODS. 



The reason for rejecting some of the methods outlined in the 

 hypothetical ideal treatment previously mentioned is, as was stated, 

 that in actual practice objections of two general kinds may be urged 

 against them. These objections are: (1) The injury to parasites or 

 eggs; (2) the unsuitability of the methods for certain kinds of feces 

 or the fact that the concentration resulting from the application of 

 the method may be too insignificant to warrant the time and effort ex- 

 pended. It will be fairly evident from the discussion of methods 

 already given just how those methods fail in these two respects, but 

 a brief summary will indicate some general truths. 



INJURY TO PARASITES. 



In regard to the first point, it is evident that if parasite eggs or 

 embryos are to be used in feeding experiments to produce infection, 

 or are desired alive for study, or if the movement of embryos is de- 

 pended upon to indicate viability or to aid the eye in detecting or 

 locating the parasites, certain methods, such as boiling (Cobb, 1904) 

 or the use of chemicals which will kill by poisoning or by rapid 

 osmosis (Telemann, 1908 ; Bass, 1909) , can not be used. Bass's ( 190!) ) 

 method has the further objection that it not only kills, but distorts. 

 Letulle (1905) urges that certain eggs, such as those of BilJiarzni 

 and Uncinaria, are mechanically injured by the use of the centrifuge. 

 I have not found this true of the eggs of the human, sheep, or dog 

 hookworm, or any other parasites encountered, but there might be 

 cases where the objection would hold good. The writer's use of shot 

 would work occasional injury to parasite material and it should l>e 

 avoided when possible. In almost all cases, the feces can be broken 

 up in a little longer time by shaking in water alone, as experiments 

 show. 



