22 THE MICROSCOPIC PREPARATION. 



the lymph, the aqueous humor, serous fluids, amniotic fluid, etc. Artifi. 

 cial indifferent fluids are much used and should always be kept in stock. 

 Of this class, the following are useful : 



1. Physiologic saline solution: A 0.75% solution of sodium 

 chlorid in distilled water. 



2. Schultze's iodized serum: A saturated solution of iodin or 

 tincture of iodin in amniotic fluid. 



3. Ranvier's solution of iodin and potassium iodid : A satu- 

 rated solution of iodin in a 2% solution of potassium iodid. 



4. Kronecker's fluid : Distilled water, 100 c.c. ; sodium chlorid, 

 5 gm.; sodium carbonate, 0.06 gm. 



5. Solution of Ripart and Petit : Copper chlorid, o. 3 gm. ; cop- 

 per acetate, 0.3 gm. ; aqua camphorae, 75 c.c. ; distilled water, 

 75 c.c. ; and glacial acetic acid, i c.c. After mixing, this solution 

 is yellow, but clears up within a few hours, and should then be 

 filtered. 



The examination of fresh tissues comes far from revealing all the 

 finer details of their structure. This is partly due to the fact that the 

 indices of refraction of the different elements of the tissues are too nearly 

 alike, in consequence of which the outlines are somewhat dimmed ; and 

 also, that changes occur, even during the most careful manipulation of 

 the tissues, which result in pictures somewhat different from the normal. 

 With many tissues and organs while yet fresh it is also somewhat difficult 

 to obtain a separation of their constituent elements. It is therefore 

 generally necessary to subject tissues or organs to special methods of 

 treatment before they may be studied microscopically with any degree 

 of profit. Certain of these methods, such as have proved by experience 

 to possess reliability, shall receive consideration in the following pages. 



METHODS OF MACERATION. 



The reagents employed for the maceration of tissues have in general 

 the property of softening or removing, partly or completely, certain con- 

 stituents of the tissues, while they at the same time harden or fix other 

 tissue elements. Generally the ground-substance or intercellular sub- 

 stance is softened or removed while the cellular or other constituents 

 undergo fixation. Tissues thus treated when subjected to teasing, 

 crushing, shaking, or brushing with a camel' s-hair brush, are readily 

 broken up into their constituent elements, giving useful and instructive 

 preparations. 



1. Alcohol, 30% (Ranvier). Dilute one volume of alcohol 



with two volumes of distilled water. Small pieces of 

 tissue are macerated in this solution in twenty-four hours to forty- 

 eight hours. It is often advantageous to fix the pieces thus 

 macerated for about an hour in -|% to i% osmic acid. Useful 

 for macerating epithelia. 



2. Dilute solutions of chromic acid, i% to -^% Small 

 pieces of tissue remain in this solution one to several days. Use- 

 ful for macerating epithelia. 



3. Concentrated aqueous solution of caustic potash. Small 

 pieces of tissue are macerated in fifteen minutes to an hour. 

 They are then transferred to a saturated aqueous solution of acetate 



