THEORETICAL IDEAL AXD PRACTICAL OBJECTIONS. 15 



which the reproductive faculty may be taken advantage of. are of 

 limited use in the examination of feces for worm parasites, as mul- 

 tiplication of the parasites under these circumstances is only pos- 

 sible in such exceptional cases as Strongyloides. 



THE THEORETICAL IDEAL. 



From the foregoing it would appear that the best technique should 

 eliminate matter of specific gravity different from that of the para- 

 sites by sedimentation, or, since it is more rapid, by centrifuging, in 

 solutions of such strengths as to get rid of the lighter nonparasitic 

 material at one time and the heavier at another; such technique 

 should eliminate matter of different size by sieving; finally it should, 

 in the course of the above processes or the filtration method, eliminate 

 matter of physical or chemical solubility different from that of the 

 parasites by the use of suitable reagents. Such a method would be 

 expected to give a slide with the maximum amount of parasitic mate- 

 rial and the minimum amount of other material. Incidentally, this 

 treatment would comminute the resultant sediment so that it would 

 give a clear, uniform microscopic field, superior to that obtained by 

 the smear method. An ordinary smear of feces, subjected to no pre- 

 liminary treatment, makes a very trashy and indifferent microscopic 

 preparation, especially in the herbivora, where large plant particles 

 are easily capable of concealing the evidences of parasitic infection, 

 and the same objection holds good to some extent of smear prepa- 

 rations of any sort of feces. 



PRACTICAL. OBJECTIONS. 



In actual practice, experience modifies the view that we should do 

 all the above things and shows that there are other things that must 

 be considered. Among these are (1) the possible injury to parasites 

 or eggs by certain forms of technique, and ( % 2) the possibility that in 

 general work certain methods may prove to have only a limited ap- 

 plication, or the concentration resulting from the application of cer- 

 tain methods may be too insignificant to warrant the time and effort 

 expended. A discussion of these points can best be given after con- 

 sideration of the writer's method. 



GROSS EXAMINATION. 



The naked-eye examination of feces for gross evidences of para- 

 sites, as stated at the beginning of this paper, receives too little atten- 

 tion, and it may be fairly assumed from the lack of statements show- 

 ing a definite technique that it usually consists of perhaps a hasty 

 glance at bottled material or possibly some picking over of the feces 

 with a dissecting needle or a stirring rod at the most. 



