360 CHAPTER XXX. 



Some persons make films by flattening blood between 

 two cover-glasses wliich are afterwards separated by sliding 

 tlie 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 favour- 

 able 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, wliich is an energetic fixative of dried films. 



Air-dried films ought to be fixed before putting into 

 aqueous or glycerin stains, else they will wash off; but this 

 is not necessary for alcoholic stains. 



718. Fixing and Preserving in Bulk. Most morphologists are 

 agreed that by far the most faithful fixing agent for blood- 

 corpuscles is osmic acid. A drop or two of blood (BiONDi 

 recommends two drops exactly) is mixed with 5 c.c. of osmic 

 acid solution, and allowed to remain in it for from one to 

 twenty-four hours. As a rule the osmic acid should be strong 

 1 to 2 per cent. Fixed specimens may be preserved for 

 use in acetate of potash solution (MAX FLESCH, Zeit. wiss. 

 Mik., v, 1888, p. 83). 



GIUUSBACH also (ibid., 1890, p. 328) combines the osmic 

 acid with certain stains. He mentions methyl green, methyl 

 violet, crystal violet, safranin, eosin, Saurefuchsin, rhodamin, 

 and iodine in potassic iodide. 



Eossi (ibid., vi, 1889, p. 475) advises a mixture of equal 

 parts of 1 per cent, osmic acid, water, and strong solution of 

 methyl green, permanent mounts being made by means of 

 glycerin cautiously added. 



EWALD (Zeit. Biol., xxxiv, 1897, p. 257) mixes three to 

 four drops of blood of amphibia or reptiles with 10 c.c. of a 

 solution of 0'5 per cent, osmic acid in 0'5 per cent, salt 

 solution (for mammals 0*6 to 0'7 per cent, salt), siphons off 

 the supernatant liquid after twenty-four hours with his capil- 

 lary siphon ( 3, p. 4), and substitutes water, alum-carmine, 

 etc., and lastly, 50 per cent, alcohol. 



WEIDENREICH (Arch. mik. Anat., Ixxii, 1908, p. 213) lays 

 a cover with a drop of blood on it on a layer of agar-agar 

 (1 per cent, in salt solution of 0*8 per cent.) and after five 



