Sprrniatogeiiesis 479 



with vaseline, and in a tew minutes, the chromatin is stained a 

 deep carmine. The entire spermatogenesis might be worked out 

 in such preparations, the only disadvantage being that the achro- 

 matic structures are not well fixed, and the preparations are not 

 permanent. Camera drawings made from the aceto-carmine 

 material, compared with those from sections of material fixed in 

 the usual reagents, show the chromosomes in the former much 

 larger in size. (Compare Fig. 198 with Fig. 205, and 201 with 

 207.) This difference is largely due to shrinkage in the usual 

 fixing fluids and alcohols. The relative sizes and positions of the 

 structures are the same in both kinds of preparations. 



If the material showed the right stages, it was put up in various 

 fixing fluids: Gilson's mercuro-nitric, Flemming's strong chromo- 

 aceto-osmic, Hermann's platino-aceto-osmic, and Carnoy's acetic 

 alcohol with sublimate. The dissecting was usually done in the 

 fixing fluid, but the small quantity of material that was dissected 

 in physiological salt solution and immediately transferred to the 

 fixing fluid, showed just as good fixation, as is shown by the clear 

 outlines of all the cell structures. A few cases of poor fixation 

 were apparently due to the long time the insects were kept in 

 captivity, as was sometimes necessary when the material was col- 

 lected several miles from the laboratory, and immediate dissection 

 was impossible. Gilson's mercuro-nitric was the fixative used 

 most frequently, because it gives excellent fixation of the chromatin 

 and is a very convenient fluid to use, but nearly all material was 

 also put in one or both of the osmic mixtures, as these give better 

 fixation of the achromatic structures. The Gilson was used for 

 two to six hours, the Flemming and Hermann for twelve to twenty- 

 four hours, followed by the same length of time in running water. 

 The Carnoy was used but little. It does not fix so well as the Gil- 

 son. Its real value is for material where an aqueous fixative can- 

 not be used. 



After fixation, the material was run through the alcohols, 

 cleared in xylol, and embedded in paraflfine with a melting point 

 of 52° C. Most of the sections were cut 5 /.< thick, a few 3^ //. and 

 6§ //. 



Many stains were tried. The three giving most satisfactory 



