86 BACTERIOLOGY. 



brane that forms in the throat. The bacillus causes 

 infection most frequently in the throat or nose, al- 

 though it may grow on the gums or about the teeth. 

 It is possible for diphtheria bacilli to cause infection 

 of the middle ear, the sinuses of the nose, and the 

 lung (pneumonia). Rarely it extends to the skin 

 about the mouth, or to the gen i tali a or rectum, 

 rphoi- The diphtheria bacillus is one of the few types 



that can be identified by its appearance under the 

 microscope, because its shape is different from other 

 bacteria. Three fairly distinct forms are recognized : 



A. The granular type, the granules generally at 

 the ends. 



B. The barred type, the granules so arranged that 

 the cell looks cross-striped like a barber's pole. 



C. The solid type, with ends often club-shaped. 



They will grow on most of the laboratory media, but 

 thrive best on media that contains blood-serum. 



It stains readily with dyes, is not motile, and 

 forms no spores. Outside the body direct sunlight 

 kills the bacilli in half an hour, but in the dust they 

 will live for months. On slate-pencils, cups, glasses, 

 or toys such as children put in their mouths, they will 

 live for weeks. 



In the nose and throat the bacilli produce, by 

 their multiplication and by the poison thrown out by 

 them, death of the mucous membrane, which appears 

 white and like a membrane. The membrane may ex- 

 tend into the nose or larynx, causing an obstruction 



