CHAPTER XXVI. 303 



missibly coarse reagent. I have, however, obtained with liquid of 

 Carnoy-Lebrun, 86, some most excellent fixations of cytoplasm. 

 The aqueous solutions of sublimate are frequently used in pre- 

 ference to liquid of Flemming on account of the facilities they afford 

 for the employment of certain stains ; but to that end I prefer 

 BOUIN'S picro-formol. 



652. Chromosomes : Chromatin Stains.* For fresh tissues, see 

 645. 



With hardly an exception modern work on chromosomes in the 

 germ-cell cycle is carried out by use of such fixations as strong 

 Flemming ( 41), Bouin's picro-formol-acetic ( 110), Carnoy ( 85), 

 or an alcoholic nitric corrosive acetic of the Gilson or Petrunkewitsch 

 type. Stains now used much are iron haematoxylin of Heidenhain 

 or Benda, thionin, safranin, well ripened Delafield, and Mayer's 

 acid hsemalum. Gentian violet is used by many. For the study 

 of the chromosomes, the desideratum seems to be some fixative 

 which will penetrate evenly and rapidly, which will strip out of the 

 cell, fats and lipoids, and which will allow the subsequent use of 

 some dense, preferably black or dark blue stain. 



Some English workers have found Flemming's strong formula, without 

 acetic acid to give beautiful results for chromosomes (e.g. L. HOGBEN, 

 Proc. Roy. Soc., B., xei, 1920). In nearly all my slides fixed for the 

 cytoplasmic inclusions ( 673) good chromosome plates are found, but 

 I consider that fixatives which contain lipoid solvents are indicated for 

 chromosome work : the preparations are thereby " stripped ' and 

 cleaner, and difficult nuclei are better interpreted when superfluous 

 materials are removed. SISTER MONICA TAYLOR (Quart. Jour. Micr. 

 Sci., 1915) stains first in thionin, mounts and studies the sections ; 

 then, if they prove to be worth it, removes the coverslip by soaking in xylol, 

 and restains in iron alum haematoxylin. Red stains are not indicated 

 because of the eye -strain they cause. 



Iron alum hcwnatoxylin is especially recommended. Dr. Lee has 

 sent me the following note on the use of this stain :- ' Some cyto- 

 logists have given up iron hsematoxylin because they have found it 

 to clog the chromosomes ; but this will not occur if the following 

 precautions are observed. Mordant sections (7 to 8 //) for not more 

 than two and a half minutes in iron alum of 2 to 3 per cent. ; wash 

 for at least a quarter of an hour ; stain in a 0-5 per cent, solution of 

 ripened haematoxylin until the sections appear dark grey, but not 

 black (about twenty-five minutes if the solution is fresh, and not 

 more than four if it has already had several slides passed through 



* By J. B. G. 



