600 INVERTEBRATES 



Dissolve the gum in the water, cold, then add the chloral and 

 dissolve with gentle heat, then add the glycerin and filter through 

 cambric in a hot funnel. 



Insect Larvae. To pass alcohol specimens to glycerin, 

 " H. J. F.," in Watson's Microscope Record, No. 9, 1926, suggests 

 the following ingenious method : Obtain a phial 1 inch in diameter. 

 Pour in glycerin 1 inch in height. Take a strip of | inch gummed 

 paper and place it outside so that its lower edge is level with the 

 surface of glycerin. Float on to the glycerin a mixture of 9 

 parts of 90 per cent, alcohol, 1 part ether, until its surface is level 

 with the upper edge of the paper. Transfer the object into the 

 upper layer with a camel-hair pencil. Evaporation should be 

 complete in twenty-four hours, when the specimen is ready, 

 mount in glycerin or jelly. 



The beautiful specimens sold by dealers in microscope slides, 

 and mounted in glycerin jelly, etc., are made as follows, patience 

 being the main requisite. Kill in weak formalin {2\ per cent.) 

 and bring into 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 18, 20, 25, 30, 40, 50, 

 60, 70, 80, 90, 100 per cent, glycerin, leaving for a day in each 

 solution, the first eight solutions being made with 2| per cent, 

 formalin, the rest with plain water. (See D. S. Spence, Watson's 

 Microscope Record, No. 25, 1932.) 



For cementing glycerin preparations see § 500. 



1189. Test for Chitin (Zander, Pflugefs Arch., Ixvi, 1897, p. 

 545). Treat for a short time with a drop of freshly prepared 

 solution of iodine in iodide of potassium and add a drop of con- 

 centrated chloride of zinc. This is then removed with water as 

 far as possible, and the violet reaction is obtained. 



P. ScHULZE {Sitz. Ges. natiir. Freunde, Hefte 8/10, cxxxv, 1921) 

 uses Diaphanol (§ 1184). If pigmented, thoroughly bleach in 

 diaplianol for at least twenty-four hours or longer. Divide the 

 material into two parts, and soak in water. Treat one part as 

 above (Zander), whereupon chitin turns violet. To distinguish 

 cellulose and tunicin from chitin treat the other part with iodine 

 and then add concentrated sulphuric acid. Chitin turns brown, 

 cellulose and tunicin blue. 



See also Webster, Zool. Jahrb., Abth. Sijst., xxvii, 1910, p. 531. 



Bethe's Stain for Chitin {loc. cii., § 1185). Sections are put for three 

 or four minutes into a freshly prepared 10 per cent, solution of anilin 

 hydrochloride, to which has been added 1 drop of hydrochloric acid for 

 every 10 c.c. They are then rinsed in water, and the slide is put with 

 the sections downwards into 10 per cent, sohition of bichromate of 

 potash. The stain is at first green, but becomes blue in tap-water or 

 alcohol containing ammonia. 



Mayer simply uses a solution of pyrogallol in alcohol or glycerin ; 

 and Hofmann {Zeit. iviss. Zool., Ixxxix, 1908, p. 684) puts for a day ox 

 more into raw pyroligneous acid. 



