Appendix B: Some Standard Reagents and Their Uses 165 



This is the so-called "strong " solution of Flemming. The mix- 

 ture should not be made until immediately before using, because 

 it deteriorates if allowed to stand for any considerable length of 

 time. The fluid is valuable for cytological work, especially for the 

 study of karyokinetic figures. Only small pieces of tissue should 

 be used, as the reagent penetrates poorly. They should remain in 

 the fluid for from 24 to 48 hours and then be washed in running 

 water for from 6 to 24 hours. From water they are transferred 

 to gradually increasing strengths of alcohol. Particles of fat are 

 blackened by the mixture. Sections stain well with safranin or 

 hematoxylin. Read the remarks on osmic acid, 20. 



12. Chromo-Platinic Mixture (Merkel's fluid). 



Chromic acid, 1 per cent, aqueous solution . . 25 c.c. 



Platinic chloride (PtCl 4 ), 1 per cent 25 c.c. 



Distilled water 150 c.c. 



This is an excellent reagent for delicate objects such as the 

 retina. Objects are left in it for from a few hours to several days. 

 Washing is done with alcohol of 50 per cent, strength followed 

 by 70 per cent, alcohol. Tissues so prepared stain well. 



13. Corrosive Sublimate (Mercuric Chloride, Bichloride of 

 Mercury). 



Corrosive sublimate is ordinarily used as a saturated solution 

 in distilled water (about a 7 per cent, sol.) or in normal saline. 

 The latter keeps better and contains a greater percentage of the 

 sublimate. Corrosive sublimate is an excellent and rapid fixing 

 fluid for many objects (glands, epithelia, etc.). Objects should 

 remain in the fluid only long enough to become thoroughly fixed ; 

 this has been accomplished when they have become opaque 

 throughout. Only a few minutes or even seconds are required to 

 fix very delicate objects, but denser tissues may require from 4 to 

 24 hours. The value of the fluid is usually enhanced by the 

 addition of 5 per cent, of glacial acetic acid. Small pieces of 

 tissue (not over 0.6 cm. in diameter) should be used where 

 practicable. Washing may be done in running water (several 

 hours) or in 50 to 70 per cent, alcohol. 



Cautions. (1) With corrosive sublimate or mixtures contain- 

 ing it, the mercuric salt is often not wholly removed in washing. 



