ZOOLOaY AND BOTANY, MICKOSOOPT, ETC. 



[309 



ordiaary pin, is introduced transversely between the lower surface of 

 the cover-glass and the square opening (fig. 42, B). This causes the 

 cover-glass to rest with equal pressure on all the nine tubes at once. 

 Thus prepared, the glass, fixed in the instrument, is exposed to 



Fig. 42. 



B 





a 



] 



d. 



J y 



a. 



U 



the heat of a spirit-lamp. The balsam is again liquefied, the ex- 

 tremity of the tubes in contact with it become attached, and it is then 

 allowed to cool. 



The varieties of powder containing diatoms are then introduced 

 into the tubes by means of a quill, and spread by a fine and very soft 

 brush on the inner surface of each tube. The operation should 

 be performed very carefully, so as not to allow particles of powder to 

 fall into the adjoining tubes. The glass is again heated, and the 

 diatoms adhere to the softened balsam in all the tubes at once — 

 after which it is again allowed to cool. Then, by raising the 

 spring 6, the cover-glass is carefully loosened, and can then be 



