220 Specific Examples of Slide Making 



should be transparent with only a faint opalescence. One of the com- 

 monest 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 that is only more or less de- 

 hydrated so that it appears faintly cloudy. If the slide does not appear 

 to be sufficiently dehydrated, all the remaining slides should be trans- 

 ferred to fresh absolute alcohol and another one tried. When it has be- 

 come 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 num- 

 ber of coverslips for which, in the present instance, a %-in. circle would 

 be admirable. 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 solu- 

 tion. Each slide is taken individually, 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 re- 

 quired to judge when the coverslip has been pushed down far enough. 

 If this is done skillfully, the surplus mounting medium will form a neat 

 ring around the outer surface of the cover. If it does not do so, care should 

 be taken that no portion of the cover is devoid of surplus mountant that 

 will be sucked under the coverslip as the solvent evaporates. 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 sur- 

 plus 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 

 Helly's fluid overnight. 



2. Wash specimen in running water for some hours. Dehydrate, clear, 

 and embed in wax. 



3. Trim block and attach to microtome. Cut ribbon of sections and 

 mount single sections or short lengths on clean slides, using diluted 

 Mayer's albumen to flatten sections. Dry thoroughly. 



