36 MANUAL OF BACTERIOLOGY. 



resisting power to strong acids. One encounters occasionally 

 bacilli that are perfectly stained side by side with others that are 

 more or less completely decolorized. These facts show the 

 necessity of practice with any method, and of exercising caution 

 and judgment in making a diagnosis where the number of 

 bacilli happens to be scanty. If tubercle bacilH are not found 

 in the first preparation, other preparations should be made. 

 Sometimes a large number of cover-glasses must be examined. 



Various expedients have been devised to concentrate tubercle 

 bacilU when only a small number may be present in a sample 

 of sputum. In Biedert's method about 15 c.c. of sputum are 

 mixed with 5 c.c. of distilled water, 4 to 8 drops of sodium 

 hydrate solution are added, and the mixture is boiled. After 

 boiling, add about 15 c.c. of distilled water. The mixture may 

 be set aside in a conical glass for from twenty-four to forty-eight 

 hours when the sediment may be collected, smeared on a cover- 

 glass and stained for tubercle bacilli; or the sediment may be 

 precipitated rapidly by the use of the centrifuge. The sediment 

 will be found to have Httle adhesive power, and will not stick 

 well to the cover-glass. It is convenient to save some of the 

 original sputum and mix it with the sediment for this purpose. 



Staining Bacteria in Tissues. — Pieces of organs about 

 I cm. in thickness may be taken. Alcohol is the best agent 

 for preserving them. The fixation will be completed in a few 

 days. It is best to change the alcohol. The amount of the 

 alcohol must be twenty times the bulk of the tissue to be pre- 

 served. 



Ten parts of the standard 40 per cent, solution of formalde- 

 hyde, with 90 parts water make a good mixture for fixation ; after 

 twenty-four hours change to alcohol. 



Imbedding in Collodion or Celloidin.— From alcohol the 

 pieces of tissue are placed in equal parts of alcohol and ether, 

 twenty-four hours; thin collodion (i| per cent.), twenty-four 

 hours; thick collodion of a syrupy consistency (6 per cent.), 



