THE DIPHTHERIA BACILLUS in 



with Gram's iodine solution, and then counter- stained 

 in Bismarck brown (see p. 50) for about a minute, washed, 

 dried, and mounted. 



The Klebs-Loffler bacillus treated by this method 

 appears a? a delicate rod, stained pale brown, and contain- 

 ing two inky- blue dots, one at each end. Sometimes a 

 dot is also seen in the centre. Most other organisms 

 simply stain brown, without any dots. (In the original 

 method the two staining solutions were alone employed; 

 Tanner introduced the use of Gram's iodine. Both 

 solutions should be filtered before use.) In some instances 

 it is possible to obtain characteristic stained preparations 

 from the cultures after five or six hours' incubation, long 

 before there is any visible growth. 



Pugh's stain consists of 1 gramme of toluidine blue 

 dissolved in 20 c.c. of absolute alcohol, and made up to 

 a litre with distilled water. Fifty c.c. of glacial acetic 

 acid are added, and the stain filtered. Cover-glass 

 preparations are stained for five minutes, and then washed 

 in water. This stain shows up the granules very dis- 

 tinctly and saves the necessity for a double stain. 



Cultural Characters. On gelatin the growth is slow, 

 without liquefaction. On agar at blood-heat growth is 

 more rapid; on potato, unless first moistened with beef 

 broth, the growth is scarcely perceptible. On blood-serum 

 and glycerin agar growth is rapid, but Loftier' s medium 

 (p. 39) is most used, as the growth which appears as a 

 cream-coloured streak along the line of inoculation is so 

 rapid as to allow the bacillus generally to outstrip other 

 organisms that may have been present in the throat, and 

 is visible in twelve hours. A number of small isolated 

 dots near to, but not touching, the actual streak is 

 suggestive of the organism. 



The bacillus exhibits heemolytic property, a yellowish 

 area encircling a colony on blood-agar. Hofniann and 

 xerosis bacilli are said to be devoid of this power. Milk 

 is turned acid without coagulation. Acid, but no gas, 

 is produced in glucose and lactose media. 



In peptone-water, after a few days, an indole reaction 

 can be obtained with sulphuric acid; this is not due to 

 indole, but to skatole-carboxylic acid (Hewlett). 



The bacillus (and some staphylococci) grows red with 

 a bluish-pink tint diffusing through the medium on a 



