BACILLUS ABORTUS 383 



would facilitate the growth of the organism. On dextrose agar the 

 colonies are round, normally colorless and transparent, and have a 

 very glistening, pearly sheen. The colonies attain a diameter of from 

 0.5 to 2.5 mm. The organism grows well on blood serum. On gelatin 

 the growth is usually very slow, probably because of the lowered tem- 

 perature of incubation. No liquefaction takes place. In milk there 

 is a moderate growth; no acid is formed, and no coagulation or pep- 

 tonization takes place. 



Conditions of Growth. The organism is killed by an exposure of 59 

 C. for ten minutes. 1 



Products of Growth. The organism produces no known ferments 

 and it produces no acid in dextrose or other sugars; on the contrary, 

 the reaction on artificial media in which the organism is growing 

 becomes slightly alkaline. The organism forms no extracellular toxins. 



Pathogenesis. Infectious abortion appears to be an infection of the 

 fetus in utero and its membranes, which results in the death of the 

 fetus and its expulsion, or less commonly its expulsion in a living 

 and enfeebled state. The time of expulsion is not definite; it may 

 occur early during the period of gestation, or it may not take place 

 until the normal completion of pregnancy. Ordinarily there is no 

 direct evidence of disease in the mother. 



The lesions in experimental guinea-pigs, which have been described 

 very carefully by Fabyan, 2 resemble both macroscopically and his- 

 tologically those of tuberculosis. As a rule, the "muscles are free from 

 lesions and there is a tendency for the organism to localize itself in 

 the perivascular or subcapsular regions of various abdominal organs. 

 The organism may persist in experimental animals for very consider- 

 able periods of time without producing manifest symptoms. Fabyan 

 has shown 3 that the organism may remain alive but latent in guinea- 

 pigs for over a year. 



Immunity. Cows which have aborted once or twice appear to acquire 

 an immunity which is supposed to be due to the formation of anti- 

 bodies in the blood. Although no extracellular toxins have been 

 demonstrated as yet, it is probable that the infected animal is sensitized 

 by endotoxins of the abortion bacillus, for such animals injected with 

 "Abortin" (an extract of the abortus bacillus) usually give a definite 

 reaction. 



Of extreme importance is the frequent occurrence of the organism 



1 Fabyan, loc. cit., p. 481. 2 Loc. cit. 



3 Jour. Med. Research, 1913, xxviii, 81. 



