48 EXPERIMENTAL DAIRY BACTERIOLOGY 



with extreme care, to avoid overheating, by holding the 

 cover glass in the fingers and passing through the flame. 

 Flood the cover glass with the mordant and heat over the 

 steam from a water bath for two minutes. Wash off the mor- 

 dant and stain for two minutes with carbol-fuchsin, placing 

 the cover over the steam. Wash, dry, and mount in balsam. 

 The number and location of the flagella should be noted. 



Exercise. From the cultures furnished make stained preparations. 

 Determine the presence or absence of flagella. 



Capsule stain.. In certain culture fluids containing al- 

 bumen or sugar many organisms produce a more or less 

 thickened cell wall. The inner side of the cell wall appears 

 as a sharp line, while the outer is less sharp and at times 

 is not to be distinguished. The cell wall absorbs a large 

 amount of water and forms a jellylike substance. In the 

 stained preparation the cell contents appear deeply stained, 

 the wall and swollen outer layer very faintly stained, or un- 

 stained. The organisms appear as though surrounded by a 

 clear zone, the capsule. Such organisms are of importance 

 in dairy bacteriology, since they are frequently one of the 

 causes of an abnormal fermentation of milk and cream, the 

 so-called " slimy " or " ropy " fermentation. 



A special stain may be used to determine the presence of 

 the capsule. Prepare the film without the use of water, air 

 dry, fix, apply glacial acetic acid, and drain off at once ; with- 

 out washing, apply carbol-fuchsin, renewing several times to 

 remove the acid ; wash in a 1-2 per cent salt solution ; ex- 

 amine in salt solution. The glacial acetic acid fixes the muci- 

 laginous capsule so that it does not dissolve in water. 



Exercise. Examine by the above method the cultures furnished you. 



Spore stain. The presence or absence of spores cannot 

 be determined by staining in all cases. Vacuoles, fat drops, 



