166 THE MICROSCOPE. 



If the stain is not sufficiently concentrated more hematoxylin 

 may be added. With hematoxylin of the strength given in the 

 formula, sections are usually sufficiently stained in from one to 

 five minutes. 



As may be inferred from what was said above, the boiling is 

 to destroy any living ferments present in the water or alum, and 

 the chloral hydrate is to prevent the development of germs 

 which accidentally reach the solution after it is made. 



No precaution is necessary in using this stain for sections, ex- 

 cept that applicable to all hematoxylin solutions, viz : after 

 staining, the surplus stain must be very thoroughly washed 

 away with distilled water ; otherwise black granules or needles 

 will appear in or upon the sections. If granules appear in the 

 preparations in spite of the washing, it will be well to boil the 

 solution three to five minutes and filter through paper or absor- 

 bent cotton. The addition of one or two per cent of chloral af- 

 ter the boiling is also advantageous. This stain has not been 

 tried for dyeing in bulk. Other substances than chloral were 

 tried, but not with so good success. For stains other than hem- 

 atoxylin, chloral might not prove so satisfactory a preservative. 



As hematoxylin is for most tissues, almost a pure nuclear 

 dye, it has been found advantageous to stain the cell body, 

 ground substance, etc., with a general or counter stain. One of 

 the most satisfactory of these is eosin, prepared as follows: 



Distilled water 50 cc. 



95 per cent alcohol 50 cc. 



Dry eosin i-iogram. 



The eosin is used after the hematoxylin in most cases, and, 

 as it is in alcoholic solution, it may be washed off with 95 per 

 cent alcohol if the object is to be mounted in balsam. If it is to 

 be mounted in glycerin or glycerin jelly, the excess of eosin 

 should be washed away with distilled water. 



An excellent counter-stain for many objects is picric acid. 

 One proceeds with this as with the eosin, except that a satura- 

 ted alcoholic solution is made and after the hematoxylin is 

 washed away a drop of the picric acid solution is added. This 

 is then washed away with 95 per cent alcohol. The time required 

 for the eosin or the picric acid to stain is very short, usually 

 onlv a few seconds. 



