CHAPTER XIX. 
THE DIPHTHERIA BACILLUS GROIT. 
The Diphtheria Bacillus. Bacillus Hofmanni. 
Bacilli Similar to the Diphtheria j Bacillus Xerosis. 
Bacillus. i Bacillus Hodgkini. 
THE DIPHTHERIA BACILLUS. 
Synonyms.— Corynebacterium diphtheriit^, Klebs-LofRer bacillus. 
Historical.— A small group of bacteria excrete soluble extracellular 
toxins which produce specific disease. The first member of the 
group to be isolated and studied was the diphtheria bacillus. Klebs^ 
called attention to the very general occurrence of a bacillus of unusual 
and characteristic appearance in the gray membranes usually present 
in the throats of severe and fatal cases of diphtheria, and a year 
later Loffler- isolated the organism in pure culture from several cases 
of the disease. Loffier also obtained the diphtheria bacillus from the 
throat of an apparently normal child, which led him to be very guarded 
in attributing a specific relationship of the organism to the disease. 
Subsequent studies by innumerable investigators have corroborated 
these observations in every essential detail, and have demonstrated 
conclusively that the diphtheria bacillus is the specific etiological 
organism of diphtheria. Roux and Yersin'' discovered the soluble 
toxin of the diphtheria bacillus and reproduced the essential systemic 
phenomena of the disease in experimental animals by injecting the 
toxin, freed from bacteria by filtration through porcelain. Y. Behring 
and Kitasato"* made the very important discovery that the blood 
serum of animals injected with gradually increasing amounts of diph- 
theria toxin contained a specific antitoxin which would neutralize the 
toxin. Diphtheria antitoxin is one of the very few specific sera pos- 
sessing curative properties. 
Morphology.— The diphtheria bacillus is one of the very few bacteria 
which possess a characteristic morphology. The organisms are 
highly pleomorphic bacilli, usually slender, straight or slightly curved 
rods with rounded and frequently swollen ends. The size and shape 
of the individual organisms vary greatly even in the same cidture; 
they are not uniformly cylindrical as a rule, but have club-like thick- 
enings at one or both ends, or they are swollen in the middle and more 
1 Verhandl. Kong. Inn. Med., Wiesbaden, II Abt., 1883, p. 143. 
2 Mitt. a. d. kais. Gesamte, 1884, 2, 421. 
3 Ann. Inst. Pasteur, 188S, 2, 629; 1889, 3, 273; 1890. 4, 385. 
^ Deutsch. med. Wchnschr., 1890, 16, 1113. 
