568 SUMMARY OF CURRENT RESEARCHES RELATING TO 



corrosive sublimate is left in the tissue and is thrown down in needles 

 when strong alcohol is added. After 24 hours the tissue is trans- 

 ferred to alcohol of 70 per cent., and after 24 hours to alcohol of 

 90 per cent., and then to absolute alcohol. With large pieces of dense 

 tissue this should be changed once or twice. After two or three days 

 the tissue is ready for staining. If time is an object, and no acid has 

 been used in the hardening, the tissue may be transferred directly 

 from alcohol of 70 per cent, to the staining fluid ; but it is advisable, 

 and in the case of delicate tissues necessary, to complete the hardening 

 process before staining. 



Staining. — Grenacher's alooholic borax carmine is used. Pure 

 carmine (2 ■ 5 per cent.) is added to the solution of borax (4 per cent.), 

 in water ; this is allowed to stand for two or three days, and occasion- 

 ally stirred — the greater part of the carmine will dissolve. To this 

 solution is added an equal bulk of alcohol of 70 per cent. This 

 mixture must stand for a week and then be filtered, when it is ready 

 for use. If on keeping more carmine is deposited, it should be 

 refiltered. 



The tissue is placed in this solution, and allowed to remain one, 

 two, or three days according to its size ; it is hardly possible to over- 

 stain, and there is sufficient alcohol in the solution to prevent injury 

 to any but the most delicate tissues. For such tissues a solution can 

 be prepared containing more alcohol, but of course less carmine, 



The tissue when removed from the staining fluid is placed in 

 alcohol of 70 per cent., acidulated with hydrochloric acid (3 to 6 drops 

 of the acid to 100 c.c. of spirit). This dissolves out all excess of 

 carmine and fixes the rest. The tissue, a dark purplish-red when 

 taken out of the borax carmine, should be left in the acidulated 

 alcohol till it acquires a bright transparent look (3 to 6 hours), it 

 may then be transferred to absolute alcohol and afterwards to tur- 

 pentine. When thoroughly permeated with this latter (the time 

 necessary varying as the size of the lump of tissue) it is ready for 

 imbedding. 



Imbedding. — This is done in paraffin, and it is exceedingly im- 

 portant to obtain a suitable paraffin. It should melt at 100° or 115° F. 

 Paraffin of various melting points should be kept in the laboratory ; 

 they may be purchased at the dealers. 



The tendency to curl up on the part of the section may be reduced 

 to a minimum by obtaining a paraffin of the proper consistency, but 

 this seems to vary according to the temperature of the room in which 

 the sections are cut. 



The paraffin must be melted in a small covered vessel in a water- 

 oven, great care being taken to keep it in a dry atmosphere. The 

 temperature in the oven should never rise more than two or three 

 degrees above the melting point of the paraffin used. 



When the paraffin is melted the tissue is removed from the tur- 

 pentine and placed in it, and this must be kept at its melting point 

 for some hours until the tissue is thoroughly permeated ; it may then 

 be poured into a paper trough, watch-glass, or any other vessel, and 

 allowed to cool. 



