20 FIXING AND HARDENING 



(b) Bouin, Zenker, corrosive acetic, Flemming-with-acetic acid, 

 etc. 



Mitochondria and Golgi apparatus rarely show after these, 

 except possibly in mammals, where these cell inclusions are 

 more resistant than in invertebrata. Fats show with the last- 

 mentioned fixative. 



(c) Osmic acid, Flemming-without-acetic, Champy, Altmann, 

 formalin, Mann's mercury-osmic liquid, Sjovall's method, etc. 

 Preserve all formed granules. (Using fluids subsequently as 

 above.) 



In section (c) the formol alone will not preserve fat ; but see 

 Sjovall's method (§ 718). 



The fixatives have not been classed according to how they 

 themselves alone affect the contents of the cell, but according to 

 how they preserve the cell preparatory to its treatment in the 

 liquids necessary for imbedding and sectioning. 



Injurious liquids which should never be used in cytological 

 fixation (3, vide supra) are acetic acid, chloroform and alcohol. 

 Acetic acid is probably the most destructive to delicate lipins, and 

 its use, except where chromosomes are being studied, is rarely 

 indicated ; any worker who uses acetic acid in his fixing mixtures 

 cannot hope to get a correct picture of any part of his cell, possibly 

 excepting the chromosomes (not the resting nucleus). The 

 most valuable fixatives are osmium-tetroxide, bichromate of 

 potassium, chromium-trioxide, and formaldehyde, possibly in the 

 order named ; the most valuable mixtures are Miiller-formol (or 

 Helly), Flemming-without-acetic, Altmann, and Champy ; the 

 three latter approach as near perfection as present-day technique 

 allows. Altmann's fluid (KgCraO, + OSO4) we find to be a 

 splendid mixture. In no case, except in small invertebrates, do 

 these fixatives (excluding formol) give a true fixation of cell 

 aggregates ; this is due to their inferior penetrating powers, and 

 to an unevenness of penetration. Small invertebrates, both 

 marine and fresh-water, and small pieces of tissues, are usually 

 exquisitely preserved in chrome-osmium mixtures, but are not 

 then generally suitable for staining and mounting whole, especially 

 for staining in carmine mixtures. 



31. Penetration of Fixatives. We cannot enter more fully into 

 the various results got by mixing globulin, albumin, etc., with 

 fixing mixtures. These experiments are reviewed in an interesting 

 manner by John Baker {Cytological Technique, 1933). But more 

 recently J. Z. Young (Nature, May 18th, 1935) has drawn attention 

 to the great improvement got in penetration of such weakly 

 penetrating mixtures as Champy and Flemming, by the addition 

 of 0-9 or 0-75 per cent. NaCl. In the Dublin laboratory, William 

 Boyle and the writer have used such " isotonic " fixatives, and 

 in some cases the improvement in penetration has been astonishing. 



