LABORATORY WORK WITH ANTHRAX ANIMALS. 289 



with dilute eosin for i to i minute. The eosin is an acid 

 anilin dye and therefore stains the protoplasm of cells, 

 nuclei, etc., but not bacteria (p. 146). Care must be taken_ 

 not to overstain the preparation with eosin, as it would 

 tend to diminish the sharp contrast that is desired. More- 

 over, the eosin is liable to decolor the violet bacilli. After 

 staining 1 with eosin, the cover-glass is thoroughly washed 

 with water and examined under the microscope. It should 

 show the deeply stained violet bacilli on a light pink back- 

 ground. If the specimen is satisfactory it can then be 

 floated off the slide, dried in the air and finally mounted in 

 balsam. 



Weigert's picro-carmin solution, or Bismarck brown 

 can also be used for contrast colors. The Gram-Weigert's 

 fibrin stain, as given in Chapter XV, can be used to advan- 

 tage where sometimes the ordinary Gram's method fails. 

 As will be seen, many important organisms are not stained 

 by this method. 



The gentian violet employed in Gram's method may be 

 substituted by other para-rosanilin dyes, such as methyl 

 violet, or Victoria blue. The rosanilin dyes, such as 

 fuchsin, methylene blue, and vesuvin will not react with 

 iodine. 



Gram's method is applicable to many pathogenic bacilli 

 and to most of the micrococci. A notable exception among 

 the latter is the gonococcus. 



The following organisms are stained by Gram's method: 



B. anthracis. B. tetani. 



B. anthracis symptomatici (p. 298). B. tuberculosis. 



B. diphtheriae. M. pneumonias crouposae. 



B. leprae. M. tetragenus. 



B. murisepticus. Moulds. 



B. oedematis maligni (p. 300). Staphylococci. 



B. oedematis maligni, No. II. Streptococci. 



B. rhusiopathiae suis. Streptothrix actinomyces. 



Yeasts. 



19 



