MS 10-MS 11 



METAL F5TAINS 



525 



pretreatment in an accelerator or mordant; 

 most metal-staining methods necessitate 

 after-treatments such as development, ton- 

 ing, and the hke. The solutions used in 

 these pre- and after-treatments, however, 

 are very much the same, whatever metal 

 be used for staining. Much space lias 

 therefore been saved by the removal of 

 these accessory ductal staining formulas to 

 Chapter 24, which should be consulted for 

 the composition of an}' solution referenced 

 "AAIS" in the formulas which follow. 



Each of the four primary divisions of 

 metal stains are secondarily divided, when 

 the variety justifies such division, accord- 

 ing to the particular compound of the 

 metal employed; all are further divided 

 according to the purpose for which the 

 technique is intended. Constant repeti- 

 tion of the formulas for "staining solu- 



tions," many of which are used in dozens 

 of techniques, has I)een avoided by plac- 

 ing such formulas at the beginning of each 

 of the subdivisions in which they are 

 employed. 



It is difficult to decide, in the case of 

 osmic acid, which of the staining formulas 

 given should be regarded as fixatives — and 

 more properly should be removed to Chap- 

 ter 18 — and which should be regarded as 

 staining solutions, which are more proj^- 

 erh' retained in the present section. The 

 author has adopted as a criterion the ques- 

 tion of whether or not any after-staining 

 solutions are to be em]:)loyed. When after- 

 staining treatment is an essential part of 

 the technique, the solution has been re- 

 moved to the division on fixatives; when 

 no after-staining is necessary, the formula 

 has been retained in this section as a stain. 



MS 10 Osmic Acid 



Osmic acid is a greatly neglected stain, 

 and there is no real justification for its 

 present retention as a reagent which is 

 used almost entirely for the demonstration 

 of the Golgi apparatus. It is not denied 

 that it does this well, but it is a pity that 

 its one-time use as a general histological 

 stain should have sunk into disrepute. 

 Osmic acid is an excellent general-piu'pose 

 stain, either for materials intended for 

 subsequent sectioning with a view to dem- 

 onstrating in class the relative distribu- 

 tion of cells, nuclei, and the like, or for 

 the preparation of wholemounts of small 

 invertebrates. Probably one of the most 

 unfortunate things that has happened to 

 the science of microtomy has been the sub- 

 stitution, for these clear gray and black 

 specimens, of the standard monstrosities 

 which are stained by convention bright 

 red, and the fuzzj^ outlines of which can- 



not compare for simplicity with those pro- 

 duced by osmic staining. 



The exact nature of the material laid 

 down when tissues are exposed to osmic 

 acid is not known; it appears fairly cer- 

 tain that it is not metallic osmium. Part- 

 ington and Huntingford (Gatenby and 

 Cowdry, 1928, 29) state that it is a hy- 

 drated form of one of the lower oxides. 

 These oxides are laid down first on unsat- 

 urated fatty acids and, later, on other 

 constituents of the cell and cell wall. Ex- 

 cess blackening may be removed either 

 with hydrogen peroxide or by the stand- 

 ard permanganate-oxalic acid techniques, 

 but in both cases fresh osmium tetroxide 

 is liberated in the tissues. This osmium 

 tetroxide must be thoroughly washed out, 

 or it will redeposit on the places from 

 which it has been oxidized. Osmic acid 

 stains are, in general, permanent. 



MS 11 STAINING METHODS 



MS 11.0 Typical Examples 



Demonstration of Golgi network 



in the ovary of the earthworm 



l)y the Ludford 1925 method 



In this, as in every other metal-staining 

 technique, the first essential is to make 



certain that all glassware is chemically 

 clean. In this instance two stopi)ered bot- 

 tles of about 25-miUiliter capacity will be 

 required, though if only a single specimen 

 is to be prepared, it will be better to use 

 the small, straight-sided, upright type of 

 stoppered weighing bottles. Both bottles 

 should be soaked overnight in sulfuric-di- 



