SECTION THREE 



picric acid, is extracted. Alternatively the picric acid can be 

 washed out with the alcohols after the tissues have been embedded 

 and sectioned. 



It is not essential that all the picric acid, which serves as a 

 mordant enhancing many staining effects, should be entirely 

 extracted from the fixed tissues. 



Remarks: 



This fixative, which keeps indefinitely and causes only slight 

 shrinkage of tissues, is compatible with almost every staining 

 technique : it is considered to be a valuable fixative for most pur- 

 poses, although it is unsuitable for kidney and mucin. Its pene- 

 tration power is great, and delicate material should be left in contact 

 with this fixative only for the minimum time, to avoid over-fixation : 

 this applies to cytological work in particular. There are many 

 modifications of Bouin, of which Allen's Fixative, B.15, has proved 

 to be the most satisfactory for chromosomes in mammalian 

 tissues. 



Bouin - Duboscq (Duboscq-Brasil, or Alcoholic Bouin) 



Recommended for : 



Arthropods containing parasites and protozoan cysts, and for 

 chitinous tissue. 



Recipe: 



Technique: 



Fix from eighteen hours to two days; then wash in 70% 

 alcohol. 



Remarks: 



This is stated to be more penetrating than aqueous Bouin and 

 for this reason it is employed for hard tissues. 



475 



