SPECIAL METHODS. 319 



e. Albuminoid granules. Become indistinct, and finally invisible, 

 on the addition of 1 per cent, acetic acid or 1 per cent, potassium 

 hydrate ; not blackened by osmic acid. 



/. Fatty granules. Not affected by 1 per cent, acetic acid or 1 

 per cent, potassium hydrate. Stained black or dark brown by osmic 

 acid. 



g. Starch. Stained dark blue to black by iodine solutions. Use 

 Gram's solution. 



h. Cellulose. Stained yellow by iodine solutions. If the water 

 be then removed and concentrated sulphuric acid introduced, the 

 color becomes blue. The w T alls of most vegetable cells are composed 

 of cellulose. 



i. Teichmann's test for haemoglobin. This test depends upon the 

 conversion of the haemoglobin or its derivatives into haemin, which 

 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 haemosiderin. The 

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



