EXAMPLE 5 



Smear Preparation of Monocystis from the Seminal 

 Vesicle of an Earthworm 



Very few Sporozoa are available for class demonstration purposes, and 

 the choice is practically limited to the inhabitants of the intestines of a 

 cockroach or to the specimen under discussion. 



The advantage of using Monocystis is that all the forms from the 

 sporozoite to the trophozoite occur in the seminal vesicle of the earth- 

 worm and, therefore, may be made available on a single smear. The de- 

 gree of infection among earthworms varies greatly, but it has been the 

 author's experience that the larger the earthworm, the more likely the 

 chance of a heavy infestation. At the same time, there is no use making a 

 great number of smears for class demonstration purposes until a prelimi- 

 nary survey of a single smear has shown that the material will be 

 satisfactory. 



There is no need to kill or anesthetize the earthworm, which is simply 

 pinned down in a dissecting tray and slit from the anterior end to about 

 the sixteenth or seventeenth segment. The edges of this slit are pulled 

 back and pinned into place, disclosing the large white seminal vesicles. 



There should be available, before making the smear, a petri dish in 

 which are a couple of short lengths of glass rod, a supply of the fixative 

 selected, an adequate supply of clean glass slides, an eye-dropper type 

 of pipette, some 0.8 per cent sodium chloride, and some coplin jars of 

 distilled water. Enough fixative is poured into the petri dish so that when 

 a slide is laid on the pair of glass rods its lower but not its upper surface 

 will be in contact with the fixative. This level should be established 

 with a plain glass slide before the smears are made. 



Now slit the seminal vesicle of the earthworm and remove a drop of the 

 contained fluid with the eye-dropper pipette. This pipette is used to smear 

 a relatively thick layer of the material on the center of one of the clean 

 slides. Before it has time to dry. lay the slide face down in the fixative 

 for a period of about 2 min. Next rinse the slide under the tap, and ex- 



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