28 STUDENTS HISTOLOGY 



not stained, but certain threads in it, which ordinarily appear as 

 granules. This part of the nucleus is called chromatin, on account 

 of its affinity for dyes. In a tissue colored with haBmatoxylin, the 

 minute granules of the nuclei are so deeply stained in the logwood 

 dye as to appear almost black. The nuclei are plainly stained, while 

 the limiting membrane of cells is usually but slightly colored. Old, 

 dense connective tissues stain feebly, or fail entirely to take color. 

 The differentiation is, without doubt, due to chemical action 

 between the elements of the dye and those of the tissue. 



A very great number and variety of materials have been used 

 for histological differentiation, and a simple enumeration of them 

 all would very nearly fill the remainder of our pages. It will be 

 found, however, that leading histologists confine themselves to two 

 or three standard formulas for general work. We shall notice only 

 those methods that have been thoroughly demonstrated by years 

 of employment as best for the purpose suggested. Special cases 

 will require special treatment, which will be indicated in proper 

 connection. 



It is important in all cases to secure the purest and most con- 

 centrated dyes obtainable. It is better to make your own solutions 

 than to buy them already prepared. 



DELAFIELD ' S H^M ATOXYLIN 



Haematoxylin crystals 4 grams. 



Alcohol 25 c.c. 



Ammonia alum . 50 grams. 



Water 400 c.c. 



Glycerin 100 c.c. 



Methyl alcohol 100 c.c. 



Dissolve the haematoxylin in the alcohol, and the ammonia alum 

 in the water. Mix the two solutions. Let the mixture stand four 

 or five days uncovered ; it should have become a deep purple. 

 Filter and add the glycerin and the methyl alcohol. After it has 

 become dark enough filter again. Keep it a month or longer * 

 before using ; the solution improves with age. At the time of 

 using, filter and dilute with water as, desired. 



EOSIN 



Eosin is an aniline dye, sold in the form of a red powder. It is 

 best to keep on hand a saturated solution in alcohol. A few drops 



