SECTION THREE 



Recipe: 



Sulphuric acid i% . . . . . . lOO ml. 



Picric acid, saturated aqueous '. . 49 ml. 



Technique: 



Wash out the picric acid with warm 70% alcohol, followed by 

 increasing strengths of alcohol. 



Remarks: 



This fixative is a powerful penetrant of chitin. 



Lewitsky's Fluid 



Recommended for : 

 Plant cytology. 



Recipe: 



Formalin (formaldehyde 40%) . . 100 ml. 



Distilled water . . . . . . 100 ml. 



Chromic acid 5% aqueous . . . . 100 ml. 



Technique: 



Fix tissue for twelve to twenty-four hours; then wash for six 

 to sixteen hours in running water. 



Marchi's Fluid 



Recommended for : 



Animal and plant tissues generally. 



Recipe : 



Potassium dichromate 2-5% aqueous 100 ml. 

 Sodium sulphate crystals . . . . i gm. 



Osmic acid 1% aqueous . . • • 50 ml. 



Note. — The last item should be added immediately before use. 



Technique: 



Immerse thin pieces of tissues, not more than 2 mm. thick in 

 the fixative for four to eight days ; then wash in running water for 

 twelve to sixteen hours. Transfer to 70% alcohol, afterwards 

 dehydrating, clearing and embedding in the usual way. 



Remarks: 



This fixative is also employed to blacken nerve fibres. 



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