CHAPTER III. 21 



does not apply to mitochondria or Golgi elements which are often 

 very badly preserved with corrosive. 



Fischer (op. cit.) says, " Many kinds of cell contents, indeed the 

 majority, have an alkaline reaction, and are thereby quite inacces- 

 sible to the precipitating action of certain agents, such as osmic 

 acid, or bichromate ; and the action of certain other fixatives, such 

 as platinum chloride or chromic acid, is more or less hindered by the 

 presence of free alkalies. For neither the chromic acid (of the 

 Flemming), nor the platinum chloride (of the Hermann) would be 

 adequate to act as acidifiers to the osmic acid of the mixtures." 



My own experience is directly contrary to these conclusions of 

 Fischer : it is common knowledge among modern workers that a 

 cell fixed in acetic acid-containing solutions has a more " raked out ' 

 appearance than when the acetic acid is omitted : this applies not 

 only to cell granules, but to the appearance of the ground cytoplasm, 

 nucleoli, and chromatin filaments. The statement that osmic acid 

 must be acidified before it will fix all parts of the cell is also contrary 

 to general experience. Formalin neutralised gives a gentler and 

 more precise fixation than acid formalin. While Fischer's results 

 may be excellent so far as concern his theoretical conclusions on the 

 fixation of weak solutions of egg-white, etc., too much attention 

 should not be paid to one who is not thoroughly acquainted with 

 practical cytology and histology. But from his very suggestive 

 observations it certainly appears that the formation of visible 

 precipitates is a very widespread, if not universal concomitant of 

 fixation ; and that the wider the precipitating power of a fixative 

 (i.e. the greater the number of organic liquids that it can precipitate), 

 the greater will be the number of artifacts to which it can give rise. 



It has lately been pointed out by some workers (e.g. UNNA, Arch, 

 f. Mikr. Anat., Ixxviii), that many of the fixing reagents come under 

 the category of oxidisers ; Unna places great importance on the 

 fact that some of the most successful fixers are oxidisers, e.g. 

 Os0 4 , K 2 Cr 2 7 , Cr0 3 ; but formalin, admittedly a splendid reagent, 

 is a reducer, while picric acid and corrosive sublimate are feeble 

 oxidisers. and that only under special conditions. 



Of ^he ten common reagents used for fixing, only four are marked 

 oxidisers, and Unna's generalities with reference to the significance 

 of oxidisers may not be the correct explanation. Generalities such 

 as made by Unna with reference to the role of oxidisers in fixation 

 resemble like claims which have been made with reference to the 

 supposed necessity for the constant use of an acid in fixatives (and 

 preferably acetic acid which is really a dangerous reagent). 



