CHAPTER III. 



GENERAL METHODS OF PRESERVING PATHOLOGI- 

 CAL SPECIMENS AND PREPARING THEM FOR 

 STUDY. 



IT is not our purpose in this section to give a complete account of 

 the technical procedures required in the study of pathological specimens, 

 since the methods are for the most part identical with those employed in 

 the study of normal tissues, with which the student or practitioner is pre- 

 sumably already familiar. We wish simply to give a few brief hints as 

 to the most useful methods for the ordinary purposes. Additional sug- 

 gestions will be found in parts of the book dealing with special tissues 

 and organs; but for the technical details of many methods which are in- 

 valuable for special purposes, one may consult the "Pathological Tech- 

 nique " of Mallory and Wright. 



The Study of Fresh Tissues. 



Although for the most part the conditions for the minute study of 

 tissues are more favorable after these have been fixed and hardened by 

 a suitable chemical agent, it is yet in many cases very important to ex- 

 amine them in the fresh state. For this purpose they may be teased 

 apart in a one-half-per-ceut solution of sodium chloride and mounted 

 and studied in the same. Sodium chloride is also useful for the separa- 

 tion by dilution of the structural elements of fluids such as exudates, pus, 

 etc. 



Rapid Fixation and Frozen Sections. 



A rapid fixation and development of detail in structural elements in 

 fluids may be secured by allowing a drop of formalin to run under the 

 cover glass and mingle with the salt solution, the flow being directed by 

 a bit of filter paper put close to the edge of the cover glass on the side 

 opposite to that on which the fixative is added. The formalin may be 

 washed out by water and the latter replaced by dilute methylene blue 

 for staining. 



When an immediate diagnosis of a solid tissue is required, useful 

 results may sometimes be obtained by a combination of the freezing 

 method with the use of formalin as a fixative as suggested by Culleu. 1 

 1 Cullen, Johns Hopkins Hospital Bulletin, April, 1895. 



