PRINCIPLES OF VETERINARY SURGERY 107 



until the nutrition is exhausted. The process requires a 

 hollow-ground slide, a large cover-glass and a bit of vase- 

 line. The vaseline is penciled around the concavity of the 

 slide, and a drop of the culture placed upon the center of the 

 cover-glass, which is then invei-ted over the concavity of the 

 slide. The drop should hang into the concavity without 

 touching the bottom. It is advisable to examine the edges of 

 the drop rather than the center, which is usually too thick. 

 Cultures grown in solid media may be examined in this man- 

 ner by first mixing a small portion of the culture with some 

 sterilized fluid. 



STAINING. — The necessity of coloring bacteria to iden- 

 tify them from other particles on the slide was recognized 

 during the earliest days of bacteriology. Carmin and hema- 

 toxylin were used until Weigert demonstrated the virtue of 

 the aniline dyes and their remarkable affinity for bacteria. 

 The number of these dyes is very large, but only a few are 

 in common use ; in fact, two or three simple stains will 

 demonstrate all the bacteria ordinarily encountered, and aid 

 in their diagnosis. 



Most of the bacteria have an affinity for basic dyes such 

 as methylene-blue, gentian-violet, fuchsin, etc. ; a very few 

 stain better in an acid solution, e. g., the tubercle bacillus. 

 They vary in their capacity for taking up the stain. The 

 glanders bacillus stains slowly, and therefore requires an in- 

 tensive dye like gentian-violet ; in case the bacteria are as- 

 sociated with blood, pus, milk, etc., methylene-blue is bet- 

 ter to use, as it does not readily over-stain. For all general 

 staining methylene-blue is the best to begin with; if neces- 

 sary, certain differential stains can be applied later. 



It is of the greatest importance that the stains used 

 should be good. Grubler's are the best. These should be 

 obtained in powder form and made up into saturated alco- 

 holic solutions from which small amounts of the aqueous 



