52 PRESERVING AND PREPARING PATHOLOGICAL SPECIMENS. 



While for many purposes other and more delicate methods of harden- 

 ing tissues are to be recommended, alcohol is most useful for most solid 

 tissues in which bacteria are to be sought : for such specimens as are not 

 quite fresh and in which the process of decay is to be immediately 

 checked, and in general for tissues in which the determination of topo- 

 graphical features for diagnostic or other purposes is the chief end in 

 view. 



FORMALIN, or formol, is the trade name for a forty-per-cent aqueous 

 solution of formaldehyde. In diluted solutions it is a valuable fixative 

 for delicate tissues. It is most commonly used in a solution of 5 parts 

 (of the commercial formalin) to 100 of water. The fresh tissues, in 

 small pieces, are put in this solution for forty-eight hours, the fluid 

 being renewed at the end of twenty-four hours. They are then trans- 

 ferred to sixty-per-cent alcohol for twenty-four hours, and the harden- 

 ing is completed with strong alcohol. 



MULLER'S FLUID which has been much used as a hardening agent 

 has the following composition : 



Potassium Bichromate, 2 parts 



" Sulphate, Ipart 



Water 100 parts 



Miiller's fluid is now most often used in combination with other 

 fixatives. 



Thus Orth's Fluid, which is Miiller's fluid to 100 parts of which 10 

 parts of comrnerical formalin are added, is a most valuable agent for 

 fixing and hardening delicate cells. The mixture should be made at the 

 time of using because it soon changes. The pieces of tissue should be 

 small, the fluid largely exceeding the tissue in bulk. The hardening is 

 completed in three or four days, when the specimens should be thor- 

 oughly washed and preserved in eighty-per-cent alcohol. 



OSMIC ACID is of great value, especially in combination, for the 

 hardening of small portions of delicate tissues, since it serves to fix the 

 elements in a nearly normal condition and stains them brown or black. 

 Osmic acid stains fat black and on this account is a valuable agent for 

 the detection of this substance in the tissues. It is generally used in 

 one-per-cent aqueous solution, the tissues, in very small pieces and when 

 quite fresh, being placed in it and allowed to remain for twenty-four 

 hours. They are now washed thoroughly in water and may be preserved 

 in eighty-per-cent alcohol. 



Flemming's Osmic Acid Mixture. For the purpose of fixing delicate 

 tissue elements to show minute structural detail, such as mitotic figures, 

 this mixture is of great value. It is made of 



One-per-cent solution of Chromic Acid, . . . . .15 parts 



Two-per-cent solution of Osmic Acid, 4 " 



Glacial Acetic Acid 1 part 



This mixture does not keep well, and hence should be made up in small 

 quantities. Small portions of tissue should soak in the mixture for 



