114 THE MICROSCOPE. [May, 



and leave it 24 hours. It will then be evenly stained (provided 

 the acid of the picric has been perfectly removed by alcohol wash- 

 ing) . To wash out over stain of l)orax carmine, immerse the spec- 

 imen for a few minutes in 70 per cent, alcohol, to which 2 per 

 cent, hydrochloric acid has been added, and in renewed washes 

 as long as color is removed by the washing fluid. Then place in 

 a considerable amount (20 vols.) of 95 per cent, alcohol, and 

 finally in absolute, and leave for several hours. At this step great 

 care is needed for the paraffine imbedding imperatively requires 

 the entire removal of water from the tissue. 



3. Imbedding. — After the water has been removed, the speci- 

 men is to be placed in spirits of turpentine and left there until it 

 becomes very translucent, all the alcohol being replaced (or chlo- 

 roform can be used equally well or, perhaps, better than turpen- 

 tine) after a period of twelve hours for a piece the size of a 

 one-half inch on a side, the specimen is transferred to a mixture 

 of turpentine (or chloroform) and parafline which is fluid but 

 nearly saturated. Here it stays another period of twelve hours, 

 when it is ready for its final bath in pure paraffine. A too hard 

 paraffine will interfere with the operation of the razor in section 

 cutting. The paraffine must be kept melted at a temperature of 

 66° C. and positively must not rise to 70° C. A water l:>ath is 

 needed for the purpose. The specimen should remain several 

 hours in this bath till all trace of the turpentine is gone by evap- 

 oration. Then the specimen can be removed and moulded in a 

 block of paraffine. If this process is wholly successful, the speci- 

 mens will keep indefinitely. I have some now which are S years 

 old and good yet, and sections can be cut out at any time. 



4. Section Cutting. — In sectionizing, the specimens should 

 be cut with a direct and not a sliding movement of the razor ; 

 the temperature of the room should be just right and the razor 

 sharpened just to the right degree and its movement at the proper 

 speed ; a slice of almost any thinness can then be cut. But all of 

 these requirements must be carefully fulfilled or exasperating fail- 

 ures are likely to occur. After the sections are obtained they 

 should be cemented to the slide. The white of egg method is 

 very easy of application. Spread a thin even film of white of egg 

 on the slide and lay the section upon it. Heat gently over a 

 lamp until the paraffine melts ; this coagulates the albumen. 

 Then set aside until the albumen has hardened. Then cover the 

 specimen copiously with turpentine and dissolve the paraffine ; 

 remove the superfluous turpentine and add Canada balsam in 

 benzine or chloroform, cover, and the section will be ready for 

 study. The sections from which the study of Lti7uhric7is were 

 prepared were made by this method, and though it is extremely 

 " kinky" it gives the most satisfactory results. 



March 3, 1892. 



