OS' THE MICKOSCOPE. . 205 



GOADBY'S FLUIDS. Goadby used two distinct fluids, desig- 

 nated by letters A and B, the difference being that alum was a 

 constituent of one and not of the other. Of both fluids there 

 were several degrees of strength, which were designated by 

 numbers. A fluid, as usually employed (A2), consisted of rock 

 salt, 4 ounces; alum, 2 ounces; corrosive sublimate, 4 grains; 

 boiling water, 2 qu irts. To make the B fluid take rock salt, 8 

 ounces; corrosive sublimate, 2 grains; boiling water, 1 quart. 



P ACINI'S FITTED. Take corrosive sublimate, 1 part; pure 

 chloride of sodium (common salt), 2 parts; glycerine, 13 parts; 

 distilled water, 113 parts. This mixture is allowed to stand for 

 at least two months. After that time it is prepared for use by 

 mixing one part of it with three parts of distilled -water, and 

 filtering it through filtering paper. This fluid is very strongly 

 recommended by Frey. It is used for blood globules, nerves 

 and ganglia, the retina, cancer cells, and especially delicate pro- 

 teinous tissues. 



CASTOR OIL. This is used for preserving certain crystals. 

 The best cold-drawn castor oil answers the purpose. 



There are a few general rules which we have found essential 

 to the successful use of these media, but which are often 

 neglected, the result being the ultimate destruction of the 

 specimens. One of the most important points is the use of an 

 abundance of the medium (we are now talking of preserving, 

 not mounting) and the gradual saturation of the object with it. 

 A piece of fresh muscle, simply mounted in a shallow cell with 

 a drop or two of Goadby's fluid, will spoil in a very short time. 

 The same object, properly treated, may be preserved indefin- 

 itely. The proper course is to completely immerse the object 

 in a considerable quantity of the liquid, and if necessary 

 change the liquid several times until the substance to be pre- 

 served has been thoroughly subjected to the action of the 

 medium. For this purpose the quantity contained in ordinary 

 cells is altogether too little; small cups, basins, large watch- 

 glasses, etc., are needed. It must be remembered that the sub- 

 stance acted upon generally absorbs certain constituents of the 

 preserving fluid, and hence the latter is left either very weak 



