106 A MANUAL OF BACTERIOLOGY 



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. Thinner and better sections are 

 obtained by the paraffin method, and for some friable 

 tissues, such as actinomycosis, it is almost essential. The 

 tissue, in suitable pieces for cutting, is transferred from 

 the diluted spirit preservative solution to 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 process 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 placed in the melted paraffin for from six to 



