74 SWINE PLAGUE 



possessed of marked variation in virulence, that is, there are 

 those that will kill a rabbit in from 1 6 to 24 hours when inoc- 

 ulated subcutaneously with a pure culture and those that 

 require from 3 to 10 days, or even weeks, to destroy life. 

 With the variations in the time period, we have corresponding 

 differences in lesions. The virulent forms produce septicemia 

 while the attenuated varieties excite a severe purulent infiltra- 

 tion about the place of inoculation and exudates on one or 

 more of the serous membranes. Conversely, it has been shown 

 that rabbits possessed of a certain amount of natural or artifi- 

 cially produced resistance will, when inoculated with a viru- 

 lent culture, die after the same period of time and with lesions 

 similar to those produced by the attenuated virus in the sus- 

 ceptible rabbit. 



• The fact that this organism is not frequently described in 

 our works on bacteriology and because of some confusion 

 existing concerning it and the bacillus of hog cholera, it is 

 deemed best to insert a short description of it here. 



§ 69. Brief description of the bacterium of swine 



plague. 



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

 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 dirtctly 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 biochetnic 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 above 37° 

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



