CHAPTER XX 
THE DIPHTHERIA GROUP 
I. Historical 
Klebs in 1883 and Loeffler in 1884 were first to dis¬ 
cover and describe the organism. 
II. Morphology 
The organisms are slightly curved rods, 4 to 5 /*, 
they are not uniform in thickness, usually being club- 
shaped. The best stain for the diphtheria bacilli is 
Loeffler’s “alkaline methylene blue,” the bacilli show 
a characteristic lack of uniformity in staining so that 
the stained preparations show lighter parts alternating 
with darker, shaded parts, the bacilli possessing a char¬ 
acteristic “beaded” appearance. It is a Gram-positive 
organism. It has no spores, capsules, or flagella. 
III. Cultural Characteristics 
The organism is an aerobic one, growing best at 37.5° 
C., although it may grow between 20° C., and 42° C. 
The best medium to grow the bacilli in, is Loeffler’s beef 
blood serum (see Chapter on The Culture Media Mak¬ 
ing). On this medium the organism show small, gray¬ 
ish white, glistening colonies. 
IV. Resistance 
The organism is killed by ten minutes’ exposure to 
58° C. Low temperatures are well borne, and it may 
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