'208 KnrosHi Ji.\sur. 



As is already known, it is difficult to obtaia good results iu tlje fixation 

 of cbromosomes in mammals. In materials which have lieen insufficiently 

 prepared, the chromosomes are usually so closely massed, that it is impossible 

 tc obtain any lesults which can be used for cytological stud}'. Consequently, 

 a? Hance ('17 b) stated, it is quite true that most of the published cytological 

 work=i on mammals are not reliable and should be carefully rejwated. 



For the fixation, therefore, several fixatives were used, namely, a modifi- 

 cation of Hance's method, FLEJlirrNO's mixture, Bouin's fluid, sulilimate acetic 

 and Champy's fluid, but the first method gave tha most satisfactory results. 



.The method of fixation used chiefly in this study is as follows: — 1. 

 T])0 luaterial u.sed must lie absolutely fresh and cut into very small pieces. 

 2. These are put immediately into Flemming's solution (weak) to which a 

 little m'ea is added ; iu this the tissues remain fi'ora twenty to twenty four 

 hours. 3. The temperature of the fixatives is about 15 degrees Centigi'ade. 

 4. Sections are bleached for from five to tnenty hours iu hjxlrogeu peroxide. 



For the fixation of the iLammalian chromosomes Haxce ('17a, b)' obtained 

 some excellent results with Fl'emming's cold strong solution which is cooled 

 to about four degrees Centigrade ; but my experience has shown that 

 Flemming's fluid, either strong or week, kept at about fifteen degi'ees Centi- 

 grade is more preferable than the cold solution. 



For the study of the chromosomes the sections were stained with Heiden- 

 hain's h'on-hsematoxyliu, and for the mitochondria also the same stain was used, 

 though the preparations were fixed in this case with Champy's fluid. The 

 mitochondria cau, however, be also difi'erentiated in the preparation fixed 

 with Flemming's strong solution to which a few drops of acetic acid are 

 added. As control Auerbach's method (methyl-green and acid-fuchsin) was 

 frequently used. This method has been found most useful as a differeutial 

 stain for chromatin and nuclejli. 



1. His explnn^llon on the notion of lUe co'.d Flemmixg's solution is ns folLiws : — " It seems 

 more probable that the explanation for the suco<ess of the cold flxntion may lie in the suppression 

 of nietiibjlic activities when the preservation of the living structures until the fluid is able to 

 jjenetrate and fix Ihem permanently." 



