CHAPTER XXIV. 255 



.y viii, 1891, p. 8 ; FERRERI, ibid., ix, 1892, p. 236 ; Bull. R. Acad. 

 Med. di Eoma, 1892, p. 67). This is said to be the most rapid method 

 ot any. Phloroglucin by itself is not a solvent of lime salts ; its function 

 in the mixture given below is so to protect the organic elements of 

 tissues against the action of the mineral acid that this can be used in a 

 much more concentrated form than would be otherwise advisable. 



ANDEER takes a saturated solution in warm water, and adds to it 5 to 

 50 per cent, of hydrochloric acid. Wash out in running water. 



Other acids than hydrochloric may, of course, be taken. ' See HAUG, 

 Zeit. wiss. Mile., viii, 1891, p. 8, and FERRERI, Bull. Acad. Med. Eoma, 

 1892, p. 67, or (for both) fifth edition. 



Desilicification. 



566. Hydrofluoric Acid (MAYER, Zool Anz., 1881, p. 593). The 

 objects are brought in alcohol into a glass vessel coated internally 

 'with paraffin. Hydrofluoric acid is then added drop by drop 

 (taking great care to avoid the fumes, which attack mucous mem- 

 branes with great energy). Small pieces of siliceous sponges will 

 be completely desilicified in a few hours, or at most a day. The 

 tissues do not suffer. 



For sponges I find that this dangerous method can be avoided. If 

 well imbedded, sections may be made from them without previous 

 removal of the spicula, which appear to break off sharp before the 

 knife. 



KOUSSEAU imbeds the objects in celloidin, as described 549, then 

 brings the block, in a covered caoutchouc dish, for a day or two into a 

 mixture of 50 c.c. alcohol and 20 to 30 drops of hydrofluoric acid, and 

 washes out the acid with alcohol containing carbonate of lithia in 

 powder. 



Bleaching. 



567. MAYER'S Chlorine Method (Mitth. Zool. Stat. Neapel, ii, 1881, 

 p. 8). Put into a glass tube a few crystals of chlorate of potash, 

 add 2 or 3 drops of hydrochloric acid, and as soon as the green 

 colour of the evolving chlorine has begun to show itself, add a few 

 cubic centimetres of alcohol of 50 to 70 per cent. Now put the 

 objects (which must have previously been soaked in alcohol of 

 70 to 90 per cent.) into the tube. They float at first, but eventually 

 sink. They will be found bleached in from a quarter of an hour to 

 one or two days, without the tissues having suffered. Only in 

 obstinate cases should the liquid be warmed or more acid taken. 

 Sections on slides may be bleached in this way. Instead of hydro- 

 chloric acid nitric acid may be taken, in which case the active 

 agent evolved is oxygen instead of chlorine. 



This method serves both for removing natural pigments, such as 

 those of the skin or of the eyes of Arthropods, and also for bleaching 



