THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



YoL. YII. 



Washington, ' D. C, November, 1886. 



No. 11. 



On the Variability of Pathogenic 

 Organisms, as Ilhistrated by the 

 Bacterium of Swine-Plague. 



BY DR. THEOBALD SMITH* 



From one of a number of spleens 

 taken from cases of swine-plague in 

 Nebraska, a bacterium was obtained 

 which resembled the bacterium of 

 swine-plague so closely, as regards its 

 morphological and pathogenic char- 

 acters, and still differed from it in cer- 

 tain minor biological features, that it 

 seemed justifiable to regard one as a 

 variety of the other, or both as varie- 

 ties of a third form. 



The bacterium was obtained as fol- 

 lows : — the spleen , though sent in ster- 

 ilized bottles, contained several kinds 

 of putrefactive microbes. By intro- 

 ducing a bit under the skin of mice, 

 in the dorsal region, a disease was 

 caused which, in symptoms, duration, 

 and lesions, was identical with that 

 produced by the subcutaneous injec- 

 tion of pure cultures of the bacte- 

 rium of swine-plague. Pure cultures 

 were obtained from these animals and, 

 by inoculating with these cultures, the 

 disease was transmitted through a 

 number of mice. As a complete de- 

 scription of the bacterium of swine- 

 plague is already on record, f I will 

 confine myself to a brief resume of 

 some important resemblances and of 

 the minor differences. 



This bacterium resembles the bac- 

 terium of swine-plague in form, size, 

 and mode of staining. Like the latter, 

 it is motile in liquid media and fails to 



* Read before A. A. A. S., Aug., 1886. 

 t Second Annual Report of the Kureau of Animal In- 

 dustry, Department of Agriculture, 1885. 

 Department of Agriculture Report for 1885. 



liquefy gelatin. Both grow alike on 

 potato and agar-agar. Both fail to af- 

 fect the microscopical appearance of 

 milk, in which they multiply. In 

 neither has spore formation been ob- 

 served. Finally, both are killed by a 

 temperature of 58° C. in from 15 to 

 20 minutes. As regards the patho- 

 genic effect, both produce the same le- 

 sions in mice, rabbits, and pigeons. 

 In these animals the lesions are very 

 characteristic and hardly to be con- 

 founded with those of other bacterial 

 diseases of the same animals hitherto 

 described. 



The differences are few and, possi- 

 bly, unimportant, but they reappeared 

 so uniformly as to leave no doubt in 

 my mind as to their constancy. The 

 one first observed was the early forma- 

 tion of a complete membrane on the 

 surface of liquid cultures. In cultures 

 of the bacterium of swine-plague a 

 complete membrane is almost never 

 seen, excepting occasionally in ad- 

 vanced cultures which have stood 

 quiet for some time. Cultures left un- 

 disturbed for a week or longer merely 

 present a whitish ring, made up of 

 bacteria, on the sides of the culture- 

 tube at the surface of the liquid. This 

 membrane is formed within 24 to 48 

 hours, whether the culture liquid was 

 inoculated from mice, pigeons, or rab- 

 bits. Two jootato cultures, one of the 

 bacterium of swine-plague, the other 

 of the bacterium under consideration, 

 grew side by side under the same bell- 

 glass, identical in color and mode of 

 growth. After several weeks a tube 

 of beef infusion peptone was inocu- 

 lated from each culture. On the fol- 

 lowing day one was covered by a mem- 



