98 METHODS USED IN THE STUDY OF BACTERIA 



Among the well-known disease-producing bacteria that are 

 positive to Gram should be mentioned Bact. anthracis, Bact. 

 pneumoniae, Bact. tuberculosis, Bact. diphtheriae, and Bacillus 

 tetanus. Among the common disease-producing bacteria neg- 

 ative to Gram should be mentioned B. typhosus, B. feseri 

 (malignant oedema), Bact. mallei (glanders), Micrococcus 

 gonorrheas, and Spirillum recurrens. 



Some species of bacteria bear the name of " acid-fast " 

 bacteria (bacteria of tuberculosis, leprosy, etc.). The proto- 

 plasm of these bacteria holds the dye even when treated with 

 strong decolorizing agents, such as mineral acids and alcohols. 

 It requires some time for the protoplasm of the bacteria to take 

 up the stain, but once combined, as with the spore, decoloriza- 

 tion is difficult. It is claimed that the high content of fat 

 accounts for the staining properties of these organisms. The 

 acid-fastness of Bacterium tuberculosis is due to a high mo- 

 lecular alcohol which has not been worked out thoroughly. 

 It is very similar to a wax according to some writers. It is 

 said to be soluble in boiling absolute alcohol. Some bacteria 

 not normally acid-fast may be made so by growing them on 

 media containing a large amount of fat. 



A special stain has been devised for the flagella. In a 

 considerable number of such stains, the mordant is tannic acid 

 and an iron salt. The process of staining flagella is one of the 

 most difficult staining processes that the bacteriologist has to 

 master, and although the methods have been greatly simplified 

 in recent years they still call for great skill and persistence. 



