CELESTIN BLUE B-EOSIN-STAINED INTESTINE 115 



have remained for five or six minutes in absolute alcohol, a single slide is 

 passed into the absolute alcohol-xylene mixture for perhaps two minutes and 

 then passed to xylene. On examination the slide should be transparent with 

 only a faint opalescence. One of the commonest faults in mounting sections 

 is to dehydrate them imperfectly. If there is any water, which has been carried 

 through the process, in the xylene (in which water is soluble to the extent of 

 about 0.2 per cent), this water will be extracted by the section which is in 

 itself an excellent dehydrating agent. There is a world of difference between a 

 perfectly cleared (that is, glass-clear) slide and one which is only more or less 

 dehydrated so that it appears faintly cloudy. If the slide does not appear to be 

 sufficiently dehydrated, all the remaining slides should be transferred to fresh 

 absolute alcohol and another one tried. When it has become apparent from the 

 examination of the test slide that dehydration is perfect, the remaining slides 

 may be run up through absolute alcohol and xylene and accumulated in the 

 final jar of xylene. 



Each section must be mounted in a solution of dried balsam in xylene. All 

 that is required for mounting is the cleaning of the appropriate number of 

 coverslips for which, in the present instance, a M-in. circle would be admir- 

 able. Again, individual preference may be consulted in the manner of cleaning. 

 The author cleans his coverslips in the same manner as he cleans his slides by 

 wiping them with a weakly acid alcohol solution. Each slide is taken individ- 

 ually, drained by its corner, and laid on a flat surface; a drop of mounting 

 medium is placed on its top. Then the coverslip is placed on the mounting 

 medium and pressed down with a needle. It should not be pressed absolutely 

 into contact with the slide, or too thin a layer of mounting medium will be 

 left. Some experience is required to judge when the coverslip has been pushed 

 down far enough. If this is done skillfiilly, the surplus mounting medium will 

 form a neat ring around the outer surface of the cover. If it does not do so, 

 care, at least, should be taken that no portion of the cover is devoid of sur- 

 plus mountant which will be sucked under the coverslip as the solvent evap- 

 orates. These slides should be left to dry at room temperature for about one 

 day and then placed on a warm plate for about a week. After they are dried, 

 the surplus dry mounting medium should be scraped off with a knife, and the 

 excess, remaining after scraping, removed carefully with a rag moistened in 

 96 per cent alcohol. 



Summary 



1. Bleed an anesthetized frog to death. Fix short lengths of intestine in 

 Petrunkewitsch's fluid for at least 1 day. 



