44 EXPERIMENTAL DAIRY BACTERIOLOGY 



Making of stained preparations. Most forms of bacteria 

 found in milk and its products can be stained by the use 

 of the simple aqueous stains. The staining is carried out as 

 follows: A clean cover glass is removed from the dish in 

 which they are stored, and placed in a pair of cover-glass 

 forceps. On the cover is placed a very small drop (size of a 

 pin head) of water by means of the platinum loop, or from 

 the glass tip of the flushing arrangement. With a sterile 

 needle a minute portion of the growth on a solid medium is 

 removed, mixed with the drop of water, and spread over as 

 large a portion of the cover glass as possible. When liquid 

 cultures are to be examined, a loopful should be removed and 

 spread over the cover glass. The preparation should be al- 

 lowed to air dry. If subjected to the action of heat, the indi- 

 vidual organisms are heaped up in concentric masses, instead 

 of being uniformly distributed. The preparation may be made 

 on the slide itself, thus eliminating the use of the cover glass. 



In order to cause the bacteria to adhere to the glass and 

 not be washed off in subsequent operations, the preparation 

 must be fixed by passing it rapidly through the upper part 

 of a Bunsen flame three times (film side up). With nearly 

 all forms this is sufficient to cause the coagulation of the pro- 

 teids of the cell and thus permit of adhesion to the glass. 

 When difficulty is experienced in fixing the preparations in 

 this way, a couple of drops of 95 per cent alcohol may be 

 allowed to evaporate from the preparation during the ordi- 

 nary fixing process. 



The forceps with the cover glass or the slide are placed 

 on the staining dish and the preparation flooded with the 

 stain, which is allowed to act from one to five minutes, after 

 which it is washed off with a stream of distilled water. The 

 wet cover glass is taken in a pair of fine-pointed forceps and 



