Appendix 179 



' CUTTING IN CONTINUOUS SECTIONS. 



' In cutting insect-sections, wliere hard cliitinous parts 

 are encountered, it is often found difficult to keep a con- 

 tinuous ribbon. This may at times be due to the imperfect 

 union of the hard paraffin and the coating of soft paraffin. 

 This coating of soft paraffin, which has long been recom- 

 mended, is very helpful in making obstinate sections 

 stick together, when it is properly a^Dplied. Immediately 

 before dipping the trimmed paraffin block into soft 

 paraffin, the upper and lower sides ^ should be touched 

 with a hot knife. By this means the soft paraffin is 

 made to adhere firmly to the block, and is not liable 

 to become detached during the cutting. 



'staining on the slide. 

 ' The sections are cemented to the slide in serial order 

 by Mayer's albumen. After melting and dissolving off 

 the paraffin with turpentine, the sections are passed 

 through the various strengths of alcohol into distilled 

 water, and then into weak Delafield's haematoxylin solu- 

 tion. This stains very slowly, and by occasionally exa- 

 mining the sections under a microscope after washing in 

 distilled water, a very precise result may be obtained. 

 The weak Delafield's haematoxylin solution will keep in 

 the dipping-bottle for a long time if a little camphor 

 is added. For nuclear differentiation Heidenhain's 

 haematoxylin will be found to give better results than 

 the above method. From distilled water the sections 

 are ti;ansferred to \ per cent, solution of haematoxylin 

 in distilled water for about an hour, and then treated for 

 the same length of time with \ per cent, solution of 

 neutral chromate of potash. Wash in distilled water, 

 dehydrate, clear in turpentine, and mount in balsam. 



1 The block is supposed to project horizontally from the holder. 



N 2 



