48 MANUAL OF BACTERIOLOGY. 



drops of sodium hydrate solution are added, and the mix- 

 ture 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 sedi- 

 ment may be collected, smeared on a cover-glass and 

 stained for tubercle bacilli ; or the sediment may be precip- 

 itated rapidly by the use of the centrifuge. The sediment 

 will be found to have little 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 hardening will be com- 

 pleted 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 preserved. 



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

 aldehyde, 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.) twenty- four hours. The specimen is laid upon 

 a block of wood and surrounded by thick collodion, and then 

 inverted in 70 per cent, alcohol. The collodion makes 

 a firm mass, surrounding and permeating the tissue, and 

 permits very thin sections to be cut. The soluble cotton 

 sold by dealers in photographer's supplies serves as well as 

 the expensive preparation known as celloidin. To make 

 collodion, dissolve it in equal parts of alcohol and ether. 

 Soluble cotton is also called pyroxylin, and is a kind of 

 gun-cotton. 



