194 Specific Examples of Slide Making 



amine it under a high power of the microscope after a coverslip has been 

 placed over the smear. It is rather difficult to see the trophozoite stages 

 in an unstained preparation, but no difficulty will be experienced in pick- 

 ing out the spore cases (pseudonavicellae) because of their relatively 

 high index of refraction. It may be assumed that adequate numbers of the 

 parasites are present if not less than three or four of these spore cases 

 occur within the field of a X 10 objective in a thick smear of this nature. 



If the worm shows satisfactory infection, the remainder of the material 

 from the eye-dropper pipette is placed in a watch glass and diluted with 

 0.8 per cent sodium chloride until it forms a dispersion about intermedi- 

 ate in thickness between cream and milk. Working as rapidly as possible, 

 as many smears as are required are made from this dilution. The dilution 

 in question will not retain the parasites in good condition for more than 

 about 5 min, but, if insufficient smears have been made in this time, it is 

 easy to take a fresh supply of the seminal fluid from another vesicle and 

 to dilute it in the fresh watch glass. The smears should be made with two 

 slides in the manner described in Chapter 11, and each slide should be 

 placed face downward in fixative for 3 or 4 min before being removed to a 

 coplin jar of distilled water. 



After they have been washed in water, the smears should be trans- 

 ferred to 70 per cent alcohol, where they can remain until they are ready 

 for staining. Any stain may be used, but it is conventional to employ a 

 hemotoxylin mixture. The method of staining is easy. The solution is 

 made in accordance with the directions given and diluted to the extent of 

 about 2 per cent with distilled water. The slides are placed in this diluted 

 solution and left until examination under the low power of the micro- 

 scope shows them to have been adequately stained and differentiated. 

 Then they are rinsed exceedingly briefly in distilled water and dried. 

 There is not the slightest necessity to employ any dehydrating agent, 

 such as alcohol, for the smears should be sufficiently thin and the objects 

 in them sufficiently well fixed that drying will not make the least differ- 

 ence. To complete the mount, a drop of the mountant selected is placed in 

 the center of each smear, a coverslip added, and the whole put on a warm 

 plate until it is dry. 



SUMMARY 



1. Make a temporary, thick smear from the seminal vesicle of an earth- 

 worm. If plenty of spore cases are present, proceed with step 2; if not, test 

 other worms until a heavily infected specimen is found. 



2. Place two glass rods in a petri dish and lay a slide across them. Pour 

 in just enough fixative to wet the lower surface of the slide. 



