50 SWINE PLAGUE 



§ 47. Brief description of the bacterium of swine 

 plague. 



Morphology. — A non-motile, rod-shaped organism varying from 0.8 

 to 2.0 microns in length and from 0.4 to 1.2 microns in breadth. The 

 ends are oval, and the shorter forms resemble micrococci. The size 

 depends upon the medium and the stage of development of the individ- 

 ual bacteria. A capsule has not been demonstrated, although often 

 there appears to be one in preparations made directly from tissues. It is 

 not observed in cultures. Spores have not been seen. Involution forms 

 are not uncommon in old cultures. They are especially numerous in 

 the organs of a rabbit when it is allowed to lie for some hours after 

 death, before it is examined. It exhibits, when stained in cover-glass 

 preparations made directly from animal tissues, a light center with 

 deeply stained extremities (polar stain). In preparations made directly 

 from cultures this character is much less marked. It stains readily with 

 the basic aniline dyes. It does not retain the coloring matter when 

 stained after Gram's method. 



Cultural and biocheinic properties. — This organism is less hardy 

 than the bacillus of hog cholera, and on certain of the media used it 

 grows very feebly or not at all. It requires a temperature of about 37^* 

 C. although it develops very slowly at the room temperature. 



Agar. — The growth on this medium is not vigorous. It is of a neu- 

 tral grayish color, with a glistening, moist appearing surface. It is 

 slightly viscid and adheres to the agar surface. Isolated colonies vary 

 from I to 2 mm. in diameter, nearly round, convex, with smooth and 

 sharply-defined margins. The condensation water becomes faintly 

 clouded with a grayish sediment which becomes viscid. Within the 

 agar the colonies appear as minute grayish dots. In agar, especially in 

 plates (Petri dishes), it emits a peculiar, disagreeable, pungent odor. 



Gelatin. — Ordinarily it does not grow in gelatin. (Dr. Theobald 

 Smith found that certain cultures grew in this medium. ) 



Potato. — It does not grow on potato. 



Bouillon. — Alkaline peptonized bouillon becomes uniformly clouded 

 in 24 hours when kept at a temperature of 36° C. Occasionally cultures 

 are obtained in which the growth appears in the form of flocculent 

 masses, but usually after a few generations these disappear and the 

 liquid becomes uniformly cloudy. If the bouillon contains any dextrose 

 or muscle sugar, its reaction becomes acid in 24 to 48 hours, owing to 

 the fermentation of the carbohydrate. With the virulent cultures the 

 liquid clears within a few daj's. The small amount of grayish sediment 

 becomes viscid after some days, and upon agitation it is forced up, 

 appearing as a somewhat twisted tenacious cone, with its apex at or near 

 the surface of the liquid. Frequently a thin, grayish, somewhat viscid 

 band composed of bacteria is found on the sides of the tube at the sur- 

 face of the liquid. It will not grow in acid bouillon. If the bouillon 



