90 A MANUAL OF BACTERIOLOGY 



of distilled water, preferably slightly warmed, to remove 

 the gum, and can then be stained at once, or may be 

 preserved in equal parts of alcohol and water. 



Bacteria seem to retain their staining properties better 

 in the tissue in bulk than in sections preserved in alcohol. 

 This objection does not hold with paraffin sections. 



(b) Paraffin method. Nothing can surpass the paraffin 

 method for the thinness and beauty of the sections obtain- 

 able by it, and for some friable tissues, such as actino- 

 mycosis, it is almost essential. The tissue, in suitable 

 pieces for cutting, is transferred from the diluted spirit 

 preservative solution to pure methylated spirit for two 

 or three hours, and then to absolute alcohol which may 

 have to be changed once unless a fairly large volume is 

 employed for from four to twenty- four hours. It is 

 then removed from the alcohol, lightly dried between the 

 folds of a dry cloth or piece of blotting-paper to remove 

 the superfluous alcohol, and placed in an excess of xylol, 

 in which it remains for from four to twenty-four hours 

 until cleared. This is recognised by the material assuming 

 a more or less semi-transparent condition, and the pro- 

 cess may be much accelerated by warming the xylol to 

 from 37 to 50 C. in the blood-heat incubator or paraffin 

 oven, the bottle containing the xylol being well stoppered. 

 When cleared it is ready to go into the bath of melted 

 paraffin. A paraffin of a fairly high melting-point is 

 perhaps the best, viz. 45 to 55 C., and is placed in glass 

 capsules in an oven which can be kept uniformly heated 

 to the required temperature. An ordinary chemical hot- 

 water oven answers the purpose quite well, and is heated 

 by a special form of small Bunsen burner with mica 

 chimney, the temperature being regulated by some form 

 of mercurial regulator, which is set a degree or two above 

 the melting-point of the paraffin employed. The tissue 

 is taken out of the xylol, blotted to remove the excess, and 



