204 STUDY OF INDIVIDUAL BACTERIA-STAINING 



form of holder necessitates the use of one hand only in secur- 

 ing the stain and dropping it on the preparation. 



The actual staining of bacteriological preparations can 

 be learned only by repeated laboratory practice, yet the 

 following methods have given such uniform results in class 

 work that it is felt they are not out of place in a text-book. 



Preparation of the "Film."— The author learned to stain 

 bacteria on the "cover-glass," but does not recall having 

 used this method in fifteen years and does not teach it to 

 his students. All staining is done on the slide. To prepare 

 a film from a solid culture medium the procedure is as 

 follows : 



First, be sure the slide is clean and free from grease. This 

 is accomplished most readily by scouring a few minutes 

 with finely ground pumice stone and a little water, then 

 washing and drying with a grease-free cloth, handkerchief 

 or piece of cheese-cloth. With the ''loop" needle place in 

 the middle of the slide a small loop of water. This is best 

 done by filling the loop by dipping in water, then tapping 

 it gently so that all that remains is the water that just fills 

 the loop level full, and this amount is placed on the slide 

 by touching the flat side of the loop to the glass. Then the 

 straight needle is sterilized, dipped into the culture and just 

 touched once into the small drop of water on the slide. The 

 remainder of the culture on the straight needle is then burned 

 off and the needle is used to spread the drop of water con- 

 taining the bacteria into a thin even film, which will result, 

 provided the slide is free from grease. This is dried and then 

 ''fixed" by passing three times through the Bunsen flame 

 at intervals of about one second, passing through slowly 

 for thick slides and a little more rapidly for thin ones. If 

 the culture is in a liquid medium, the use of the loop of water 

 is unnecessary; a loop of the fluid from the surface, middle 

 or bottom as the culture indicates, is spread out to a thin 

 film dried and fixed. 



After the film is fixed the stain desired is dropped on, 

 allowed to act for the proper time, which will depend on the 

 stain and the preparation, washed in water, dried thoroughly 

 and examined with the oil-immersion lens, without a cover. 



