i8o Appendix 



' CELLOIDIN SECTIONS. 



'By the celloidin- embedding method very thick sec- 

 tions may be cut. Larvae fixed by tlie chromo-nitric acid 

 metliod are stained in a borax-carmine sohition for at 

 least a week. After washing in acidulated alcohol and 

 dehydrating, they are placed in a mixture of equal parts 

 of absolute alcohol and ether for a few hours. A thick 

 solution of celloidin in the same mixture should then be 

 added, a few drojDs at a time, at intervals of a few hours, 

 until the consistency of a thick syrup has been reached. 

 The contents of the bottle are then poured into a paper 

 tray, and the larvae arranged in the desired position by 

 means of needles wet with the mixture of alcohol and 

 ether. The tray is allowed to stand for about ten minutes, 

 until the surface has set, and is then submerged in 80 per 

 cent, alcohol for a day. The paper is now removed, and 

 the celloidin mass cut up into blocks, which are carefully 

 trimmed. These may be kept in 80 per cent, alcohol 

 until required to be sectionized. To fix the celloidin 

 block upon the object-holder of the microtome (or upon 

 any wooden holder to be clamped in the microtome), pour 

 a few drops of a celloidin solution upon the surface of the 

 holder. Dip the celloidin block into a little ether in 

 a watch-glass, and then press it firmly upon the holder. 

 Allow it to stand for a few minutes, and then place it in 

 80 per cent, alcohol for a few hours. The sections should 

 be made with a long slicing cut, the razor and the 

 celloidin block being kept well wetted with spirit. The 

 sections are arranged in serial order, close together,, upon 

 two or three slides, and the excess of 80 per cent, alcohol 

 is removed with blotting-paper. To fix the sections to 

 a slide, place in a covered dish (a Petrie's dish answers 

 very well) with a little ether in the bottom. In a few 

 seconds the celloidin in which the sections are embedded 



