104 A MANUAL OP BACTERIOLOGY 



fixed thereby. In all cases the fixing fluid should be used 

 in considerable excess. Fixing fluids containing potas- 

 sium bichromate (as in Miiller's fluid) and chromic acid 

 tend to prevent the bacteria from staining with any 

 certainty, and should be avoided. 



Section Cutting 



In order satisfactorily to demonstrate bacteria in 

 tissues and their relation to the tissue elements, it is 

 usually necessary to prepare sections. For this purpose 

 either the freezing or the paraffin method should be 

 employed. 



(a) Freezing method. The tissue, in suitable pieces, 

 must first be soaked in water to remove the alcohol. A 

 convenient way of doing this is to place the material in 

 a wide-mouthed bottle, into the mouth of which an 

 ordinary glass funnel is introduced, and the bottle with 

 the funnel is placed under a stream of running water ; 

 the funnel, while allowing the water to flow out, retains 

 the pieces of tissue in the bottle. With running water 

 the alcohol will be completely removed in from one to 

 two hours ; in still water, which should be changed two 

 or three times, this result may not be attained for several 

 hours, during which time there is an ever-increasing risk 

 of bacterial contamination from without. It is essential 

 to remove all the alcohol, or the tissue will not freeze. 



When the alcohol has been removed, which is known 

 by the tissue sinking in the water (lung is an exception- 

 it always floats unless solid from any cause), the pieces 

 are transferred to a strong mucilage of gum acacia : 



Gum acacia ..... 5 grm. 

 Cane sugar ..... 0-5 grm. 



Water 100 c.c. 



Add apiece of thymol or a little carbolic acid to prevent decom- 

 position. Hamilton saturates the solution with boric acid. 



