36 ESSENTIALS OF BACTERIOLOGY. 



Pieces of the tissue one-quarter inch in size are covered with 

 alcohol for 24 to 48 hours. 



When hardened it must be fixed upon or in some firm object. 

 A paste composed of- 

 Gelatine 1 part. 



Glycerine 4 parts. 



Water 2 parts. 



will make it adhere firmly to a cork in about 2 hours, or it can 

 be imbedded in a small block of paraffine, and covered over with 

 melted paraffine. 



Cutting. The microtome should be able to cut sections j^j, 

 inch in thickness ; this is the fineness usually required. 



The sections are brought into alcohol as soon as cut unless 

 they have been imbedded in paraffine, when they;ire first washed 

 in chloroform to dissolve out the paraffine. 



Staining, All the various solutions should be in readiness, 

 best placed in the little dishes in the order in which they are to 

 be used, as a short delay in one of the steps may spoil the speci- 

 men. 



FIG. 12. 



Spatula for Lifting Sections. 



A very useful instrument for transferring the delicate sections 

 from one solution to another is a little metal spatula, the blade 

 being flexible. 



A still better plan, especially when the tissue is "crumbling," 

 is to " carry out" the whole procedure on the glass-side. 



General Principles. The section is transferred from the alco- 

 hol in which it has been kept mto water, which removes the 

 excess of alcohol, from here into 



Dish I, containing the stain; where it remains 5 to 15 minutes. 

 Then- 



Dish II, containing 5 per cent, acetic acid (I to 20) ; where it 

 remains to 1 min. The acid removes the excess of stain. 



