336 TEXT-BOOK OF BACTERIOLOGY. 



XXVIII. CHICKEN-CHOLERA BACILLUS. 



We have thus far discussed only diseases which affect man ex- 

 clusively, like the cholera, or affect him principally, as tuberculosis, 

 or under certain circumstances, as anthrax. We will now consider 

 a series of affections likewise caused by micro-organisms but con- 

 fined to the animal kingdom. 



There appears among- the poultry kept in yards, especially 

 among the fowl and geese, a very destructive, murderous plague, 

 the symptoms of which remotely resemble those observed in gen- 

 uine cholera of man, for which reason it is called chicken cholera 

 (cholera des poules). Perroncito, and after him Pasteur, demon- 

 strated the presence of bacteria in the blood, organs, and excreta 

 of affected animals. Pasteur cultivated them artificially outside of 

 the body and, being able (in 1880) to reproduce the disease from 

 cultures, he furnished the incontestable proof of the causative sig- 

 nificance of the micro-organisms. 



They are small, rather short but broad rods with rounded ends, 

 immobile, frequently met with in unions of two, more rarely in 

 long threads of greater numbers. Pasteur described them as 

 micrococci and it requires really good lenses and staining to ascer- 

 tain their true form. 



A very peculiar property of the bacilli will be noticed in stain- 

 ing: the single cells take up the colors readily only at the ends, 

 while the middle part remains unstained and appears as a bright 

 gap between the two darker, poles. Only close observation will 

 show the existence of this intermediate connecting link and prevent 

 the error of regarding the stained ends as independent structures 

 as micrococci. This phenomenon is most clearly perceived when 

 the preparations are stained with methyl-blue. The bacteria can- 

 not be prepared by Gram's method, since they are decolored in con- 

 tact with iodine. 



Sporulation has, as yet, not been observed with certainty in this 

 germ ; but it is a remarkable fact that they possess a rather high 

 power of resistance to external influences. They can, for instance, 

 pass the stomach without being destroyed by its acid. 



These bacilli thrive at ordinary, as well as at breeding temper- 

 ature and belong to the semi-anaerobic kinds. 



On the plate the colonies appear about the third day, as small 

 white dots at the bottom of the gelatin. They advance to the 

 surface but slowly, and never reach a large size. The gelatin 

 is not liquefied. Microscopic examination exhibits them as irregu- 

 larly-rounded discs with sharp, smooth edges of yellowish or yel- 



