34 METHODS OF EXAMINATION. 



transferred to water, and afterwards to Weigert's solution of picro- 

 carmine for half an hour. 



They are further washed first in water, then in alcohol, are clarified 

 with clove oil, and mounted in balsam. By this method the nuclei are 

 stained red and the bacilli violet ; the carmine has replaced the 

 gentian violet in the nuclei, but has had no effect upon the violet 

 taken up by the bacilli. In a similar manner, a solution of iodine and 

 iodide of potassium does not remove the basic colours from micro- 

 organisms, but it rapidly decolorises nuclei and other tissues. It is 

 upon this fact that Gram's method is founded. 



For staining most bacilli and micrococci a saturated watery solution 





~,r<l 





NT ' 



. 1/ 



'/ 





Fig. 4.— Blood of a mouse killed by mouse-septictemia. Blood 

 dried, heated, and stained with methyl blue, and mounted in 

 glycerine. ( x 700.) 



a. White blood corpuscle with horse-shoe-shaped nucleus, and 



numerous minute bacilli in and around it. 



b. Red blood corpuscles. 



c. Small bacilli between corpuscles. 



of gentian violet or methyl violet (ten minutes), methyl blue (thirty 

 minutes), or Bismarck brown (twenty-four hours) may be used. The 



