SPECIAL METHODS. 437 



crystallizes in rhombic plates of a reddish-brown color. The haemin 

 is produced by heating with a little salt and strong acetic acid. 

 Evaporate a drop of neutral salt solution to dryness on a slide. 

 Place the substance to be tested upon it and cover. Fill the space 

 between cover and slide with glacial acetic acid and heat over a 

 flame till bubbles begin to form. Maintain that heat for a few 

 minutes, replacing loss by fresh additions of acetic acid. Let the 

 slide cool slowly, and, when cold, examine. If the results are nega- 

 tive, repeat the heating with acetic acid. The acid should not 

 actually boil, but should be kept at the point of incipient ebullition. 



j. Tests for amyloid substance. Sections of fresh tissue may be 

 soaked for some time in Gram's solution, then washed and examined 

 in water. Amyloid substance is stained reddish-brown, the tissues 

 yellow. Sections of tissues fixed in alcohol, corrosive sublimate, or 

 formaldehyde, may be stained in a solution of 1 per cent, methyl- 

 violet dissolved in distilled water, without the addition of alcohol. 

 The sections are then washed in 1 per cent, hydrochloric acid for 

 the purpose of differentiating the stain. After thorough washing 

 in several changes of water they may be mounted in glycerin-jelly. 

 The amyloid substance is stained reddish-violet, the other tissues 

 blue. 



k. Test for iron in pigmentations. The iron from the haemo- 

 globin of the blood is sometimes present in the pigmentation result- 

 ing from old extravasations, in the form of hsemosiderin. The 

 same compound is also sometimes found in the tissues in cases of 

 pernicious anaemia. The presence of iron in this pigmentation may 

 be demonstrated by the following method : 



(a) The tissues should be fixed in alcohol. 



(6) Soak the section in a 2 per cent, solution of potassium ferro- 

 cyanide for ten minutes. 



(c) Transfer to Orth's acid alcohol (page 422) for five or ten 

 minutes. 



The sections may now be examined in a glycerin-mount with a 

 wide diaphragm, or they may be counterstained, for which purpose 

 treat as follows : 



(d) Wash with water. 



(e) Stain with Orth's lithio-carmine. 



(/) Dehydrate and mount in xylol-dammar. 

 The iron in the section is converted into Prussian blue ; the nuclei 

 of the cells, when the counterstain has been employed, are red. 



