6lO MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



of typical membranes. The organisms were isolated and differentiated 

 in 1884 by Loeffler, who was able to fulfill Koch's postulates for patho- 

 genic microbes. Accidental infection of the human being has happened 

 in the laboratory and confirmed the findings of animal inoculation. The 

 success of antitoxin treatment is further evidence of causal relationship. 



The organism is detected in the following manner: A sterile swab is rubbed gently 

 over the inflamed area or against any visible membrane, care being taken to touch other 

 parts as little as possible. The swab is then immediately inserted into a tube of 

 specially prepared medium Loeffler's inspissated blood serum over the surface of 

 which it is rubbed back and forth. The swab is returned to its own tube or left 

 against the serum and the culture and swab sent to the laboratory. After twelve to 



FIG. 104. Bacterium of diphtheria. Xiooo. (After Williams.) 



eighteen hours of incubation, at 37, smears are made from the cultures and stained 

 with Loeffler's methylene blue. The diagnosis is made on the morphological characters 

 of the bacterium. Occurring in pure cultures the form of the bacterium is subject 

 to remarkable changes according to the medium and length of cultivation. Its size as 

 it appears in exudates and from serum media varies from ifi to 7/1 in length and 

 0.25^1 to 2/j. in width. The rods are straight or slightly curved, usually not uniformly 

 cylindrical but with swelling at the ends, or in the middle, or irregularly disposed (Fig. 

 104). Both ends may be rounded or both pointed, or one rounded and the othe r 

 p ointed. Branching forms are not infrequently found. The bacteria may appear in 

 pairs end to end; more frequently and typically they are inclined to one another at a 

 greater or less angle and may assume a parallel arrangement or the form of a short zig- 



