392 STAINING MICROSCOPIC OBJECTS [Ch. XI 



imbedded first in collodion so that there wiU be a tough matrix to 

 hold the parts in place, and then for ease and rapidity of sectioning 

 paraffin imbedding is added. 

 Steps in double imbedding: 



1. Fix in any desired way. 



2. Dehydrate with absolute alcohol half a day or more. 



3. Put into ether alcohol half a day or more. 



4. Put into 1% coUodion half a day or more. 



5. Put into 25% collodion i to 2 days. 



6. Put into s % coUodion for one day or longer. 



7. Imbed in the s % coUodion, using a paper box (fig. 221). Take 

 the precaution to Ughtly vaseUne the inside of the paper box (§631, 



657). 



8. Float the imbedded tissue on chloroform in a glass dish. 



9. When the collodion is hardened by the chloroform, remove the 

 paper box and transfer to the castor-xylene (§ 554) clarifier to finish 

 hardening and clarifjdng the coUodion mass. 



10. Put into melted paraffin for infiltration. Leave in the infil- 

 trating oven (fig. 220) a day or two. There is some advantage, 

 according to some, in transferring to pure xylene or to cedar-wood 

 oil for half a day before putting into the imbedding paraffin. Sec- 

 tion in ribbons as with paraffin (§615). 



The sections are spread and stained exactly as for the paraflSn 

 method, except that carmine cannot be used without staining the 

 coUodion. 



Staining and Permanent Mounting 



§ 638. Generalities on stains. — From the standpoint of the object 

 to be stained, dyes may be divided into two great groups: 



(i) (a) Those which select out or differentiate certain parts of 

 the tissue and make them prominent. Such dyes are called then 

 differential or selective. If the nucleus is the part selected, the dye is 

 frequently caUed a nuclear dye. 



(fi) General or counter stains. These stain all parts of the tissue, 

 and are usuaUy contrasting in color; blue or purple and bright red 

 are frequent combinations, e.g. hematoxylin and eosin. There is an 



