The Paraffin Method 



103 



and other material for a study of mitotic figures, it is necessary that 

 killing be very prompt. In a weak solution of chromo-acetic acid, 

 nuclei which have begun to divide may complete the division, 

 although the reagent might hinder nuclei from entering upon division. 

 By treating for 20 minutes to 1 hour with Flemming's weaker 



FIG. 19. Spencer rotary microtome with electric motor and Land's apparatus for 

 temperature control. 



solution, or with a chromo-acetic solution containing a much smaller 

 proportion of osmic acid, the killing will be greatly accelerated and 

 the proportion of nuclei in division will be correspondingly greater. 

 If filamentous algae are placed for 10 or 20 minutes in a chromo- 

 acetic solution containing a little osmic acid, all the advantages of 

 immediate killing will be secured. Material is then transferred to 

 chromo-acetic acid containing no osmic acid. The short treat- 

 ment with an osmic solution is not likely to cause any serious 

 blackening. 



