3S Till-: AMKKICAN MONTH I, V [ Fol.ni:irv, 



to forty or fifty times the volume of tlie specimen. There is 

 only one exception — when the fixritives are powerful :uul ex- 

 pensive (osmic acid). 



Aico/tol. — Three ci>ncentratii»ii> au- u>c(i : Ran\ icr's ^ alcohol, 

 equally excellent for dissociating; and for lixinjj. It is made of 

 alcohol, 36^ C., one volume, with two volumes of" water. Alcohol 

 of 90" is used daily in pathological anatomy. Portions of tissue 

 not exceedintj a square centimetre are suspendeil in it by a thread. 

 A tissue capable of contracting — a hit of skin, for instance — 

 is spreail on the bottom of a dry saucer, anil while it is held with 

 two needles yo'^ alcohol is poured over it : in a few moments the 

 needles are removetl. for then the skin will not contract. This 

 rule shoidd be observed, otiierwise we are apt to have deformed 

 specimens or those which cannot be cut in any selected direction. 

 Although good preparations maybe made of specimens that have 

 been long in alcohol, it is better to take them out in from 24 to 

 4S hours. Absolute alcohol is rarclv used as a fixing reagent. 

 Specimens siiould not be left in it for more than a dav or the} 

 will not stain well. 'I'lie beginner should piocure the one-third, 

 the 90"^, and the al)solute alcohol. 'J'he last is exceedingly useful 

 for many purposes 



Ostttic Acid. — This is the lixative par cxccllcticc As 



the cost is great and since the solution is unstable, the latter 

 should be made with certain precautions. A white or vellow 

 glass bottle is washed with sulphuric acid. (It is not the light 

 but organic matter that reduces the solution. The bottle should 

 have a glass sto])per.) Rinse with distilled water to remove every 

 trace of acid. The little tube containing the osmic acid is well 

 washed in alcohol. nicke<l with a lile. and glass and acid are put 

 into the bottle. Aild ^o c. c. of distilled water. A i per cent, 

 solution is generallv used. If the cleansing has been perfect the 

 solution will remain clear. It is used as a vapor or in solution. 



Fixation bv the vapor is easiest and most efficacious for small 

 objects. With free elements — blood, for instance — invert the slide 

 over a wide-mouthed bottle in which is a little osmic acid. In a 

 few minutes the fixation is perfect, and the preparation can be 

 stained and mounted. Larger objects (not exceeding i mm. 

 square) and membranes are fastened by pins to a cork which then 

 stops a wide-mouthed bottle containing i c. c. of osmic acid. 

 Fixation is here slower. The acid should be allowed to act foj" 

 from ID to 15 minutes or even longer. Wash iapidly in distilled 

 water, stain or keep in alcohol for sectioning. When a tissue is 

 placed directlv in the i per cent, solution, the specimen, wc re- 

 peat, sho'.dd be as small as possible (i mm.). In a bottle with 

 ground-glass stopper place 2 c. c. of the .solution. The tissues 

 remain therefor a variable time ; 6 hours are usually sufHcient. 

 The specimen should be carefullv washed in many waters till all 

 odor has been removed ( 10 to 12 hours) ; preserve in "jo^ alcohol. 



