CHAPTER XXX. 



BLOOD AND GLANDS. 



Blood. 



781. Fixing and Preserving Methods. The school of Ehrlich used 

 to fix by heat. A film 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. But I 

 believe they have now well-nigh abandoned this barbarous practice. 



In wet methods either the 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 a perfectly 

 clean slide. Bring down on to the slide the edge of another slide 

 held over it at a slope ; move this along till 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, and the blood will 

 follow it and be drawn out into a film without being crushed. Simi- 

 larly 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. 



Some persons make films by flattening blood between two cover- 

 glasses which are afterwards separated by sliding the one over the 

 other ; but that produces an injurious kneading of the cellular 

 elements. 



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. 



