294 THE ESSENTIALS OF HISTOLOGY. 



structed, and works with great accuracy. In all cases it is most important 

 that the knife should be in perfect order. 



Staining and Mounting of Sections. The fluids most commonly em- 

 ployed for the staining of sections are : 1. A solution of hsematoxyliri and 

 alum ; 2. a solution of carmine ; 3. a solution of picro-carminate of ammonia. 

 The time of immersion in the staining fluid varies according to the strength 

 of the fluid and the mode by which the tissue has been hardened. The neces- 

 sity of staining sections may be avoided if the piece of tissue is stained in 

 bulk before embedding. For this purpose either Delati eld's or Ehrlich's 

 lumnatoxylin may be used. If Delafield's be employed the piece of tissue is 

 left to stain for 24 hours or more, and is then placed for 15 to 30 

 minutes, according to thickness, in alcohol containing 1 part of nitric acid per 

 cent. The excess of stain is thereby removed and the sections are rendered very 

 clear and distinct in all their details. If Ehrlich's is used, the pieces of tissue 

 should be thoroughly washed in tap-water for an hour or more and then 

 transferred to alcohol. For some purposes an alcoholic solution of magenta 

 is used for staining in bulk ; from this the tissue goes into a small quantity 

 of oil of cloves, and after being soaked with this it is passed through turpentine 

 into the melted paraffin. 



If the tissues have not been stained in bulk, the following is the order of 

 transference of the sections (they are supposed, if cut from paraffin, to have 

 been freed from this by immersion in turpentine or xylol) : 



1. From turpentine to absolute alcohol (5 minutes). 



'2. From alcohol to distilled water (^ minute). 



3. From distilled water to hsematoxylin, which for staining purposes should 

 be diluted with distilled water and filtered (5 minutes or more). 



4. From hsematoxyliu to distilled water (^ minute). 



5. From distilled water to alcohol (2 or 3 minutes). 



6. From alcohol to oil of cloves 1 (1 minute). 



7. From oil of cloves to Canada balsam solution. 



If the tissues have already been stained in bulk, the sections are simply 

 mounted in Canada balsam after the paraffin used for embedding has been 

 dissolved away from them in turpentine or xylol. 



Adhesive methods of mounting. Friable sections, such as sections of small 

 embryos, and ribands of sections such as are cut with many microtomes, may 

 be mounted in the following way : The slide is smeared with a solution of 

 shellac in clove-oil, the sections are placed in this and warmed so as to melt 

 their paraffin. They are thus fixed by the shellac, and the slide can be im- 

 mersed in turpentine to remove the paraffin, and the sections then covered in 

 Canada balsam. For this method the tissue should have been previously 

 stained in bulk. 



A simpler method, but one which answers the purpose very well, is to place 

 the riband or pieces of paraffin containing the sections on the surface of warm 

 water (not hot enough to melt the paraffin), to float the sections on to a slide, 



1 Other essential oils, such as oil of cedar, oil of bergamot and xylol, may be used 

 instead of oil of cloves. 



