CHAPTER XXXIV 

 BLOOD AND GLANDS * 

 BLOOD 



868. Fixing and Preserving Methods. The school of Ehilich 

 used to fix by heat. A fihn of blood was spread on a cover-glass 

 and allowed to dry in the air, and then fixed by passing the 

 cover a few times, three to ten or twenty, through a flame, or by 

 laying it face downwards on a hot plate kept for several minutes 

 or as much as two hours at a temperature at which water not 

 only boils, but assumes the spheroidal state (110° to 150° C). 

 For details, see Gulland {Scottish Med. Journ., April, 1899, 

 p. 312 ; Rubinstein, Zeit. wiss. Mik., xiv, 1898, p. 456 ; Zielina, 

 ibid., p. 463). At the present day heat fixation is only used as 

 a preliminary to staining with the Ehrlich-Biondi mixture, § 322. 



In wet methods either blood is mixed at once, on being drawn, 

 with some fixing and preserving medium, and studied as a fluid 

 mount, or films are prepared and put into a fixing liquid before 

 they have had time to dry, or after drying in the air without heat 

 for a few seconds (at most ten to thirty). 



To make a film, place a very small drop of blood on the convex 

 side of a perfectly clean slide. Bring down on the slide the edge 

 of another slide (or No. 2 coverslip) held over it at an angle of 

 45 degrees ; move this along until it touches the edge of the drop 

 and the blood runs along the angle between the two slides. Then 

 move the second slide away from the drop, pressing lightly on 

 the first slide, and the drop will follow it and be drawn out into 

 a film without being crushed. Well-spread films should show 

 the red cells almost touching but with no overlapping. Similarly 

 with two cover-glasses, to make a cover-glass film, which can be 

 floated face down on to fixing or staining liquids in a watch-glass. 



Most of the usual fixing agents are applicable to blood. But it 

 is often necessary to employ only such as are favourable to certain 

 stains. Those most recommended in this respect are alcohol, 

 formol, sublimate (should not be too strong), osmic acid in very 

 light fixation, or absolute methyl alcohol, which is an energetic 

 fixative of dried films. 



Air-dried films ought to be fixed by prolonged heating or 

 corrosive sublimate before putting into aqueous or glycerin 



* By E. S. D. 



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