HARDENING AND FIXING REAGENTS. 



the eye. It penetrates evenly and thoroughly, so that large 

 pieces can be hardened in it, while at the same time it has 

 no tendency to over-harden and render the tissues brittle. 



The disadvantages attaching to all the Bichromate solutions 

 are that they discolour the tissue more or less. A long time 

 is required for the hardening, and if tissues be kept in them 

 too long they sometimes produce netlike forms of coagula- 

 tion, or deposits of a dark granular precipitate in the cells 

 and intercellular substances ; they are apt to develop moulds. 

 They dissolve out calcareous deposits. 



When the nervous system is stained by Weigert's method, 

 the tissue must be hardened in this or one of the other 

 Bichromate solutions. 



It is unsuitable for hardening tissues to be examined for 

 the amyloid reactions or for bacteria. 



Tissues ought to be placed in at least 20 times their bulk of 

 " Miiller." This must be changed after 24 hours, again after 

 3 days, and then once a week for the next 6 weeks. Even for 

 small pieces 6 weeks in all are generally required. The 

 tissues, after removal from " Miiller," are soaked in 50 p. c. 

 Alcohol from 1 to 2 days, then 70 p. c. Alcohol for a similar 

 time, and finally placed in 90 p. c. Alcohol, which should be 

 changed occasionally so long as it becomes coloured. In the 

 case of large masses, a preliminary washing in water will save 

 Spirit and do no harm. 



(iv.J) MULLER'S FLUID AND SPIRIT. 



Midler's Fluid, 3 ; 90 p. c. Alcohol, 1. 



This is usually directed to be cooled before using it, but as there is only 

 a rise of 11 E. on mixing- them, the precaution is hardly necessary. 



Used in the same cases as " Miiller," only its action is more 

 rapid. It takes about half the time of " Miiller" to harden 

 tissues. Whilst hardening in this, and during the subse- 



