MICROBIAL DISEASES OF MAN AND DOMESTIC ANIMALS 759 



occurred, a small bacterium which he was able to grow in pure culture, 

 and, by inoculating pure cultures of this organism, he produced the 

 disease in cows, sheep, goats and rabbits. 



The microbe is a short non-motile rod, staining with moderate ease, 

 and decolorized by Gram's method. It does not form spores but the 

 vegetative forms are fairly resistant to drying and may, perhaps, live 

 for some weeks under ordinary conditions in pastures and stables. Its 

 artificial culture requires special technic because of its pecuUar oxygen 

 requirement. The bacterium usually fails to grow in the presence of the 

 atmospheric air or under anaerobic conditions. It requires for its de- 

 velopment a partial pressure of oxygen somewhat less than that of the 

 atmosphere. When inoculated into deep serum-gelatin-agaf tubes and 

 incubated in the air, the colonies develop only in a particular zone 

 about five milhmeters beneath the surface of the medium. When cul- 

 tures are placed in the proper atmosphere, development on the surface 

 may be obtained. Prolonged cultivation on artificial media obscures 

 this pecuUar property of the microbe so that old culture strains grow 

 well under ordinary aerobic conditions. 



In the diseased animal, the specific bacteria are found in the pla- 

 centa and amniotic fluid, frequently also inside the foetal intestine, 

 sometimes in the tissues of the foetal organs, and in the wall of the 

 maternal uterus. The placenta appears to be the particular organ 

 favorable to the development of the germ, and when this has been 

 discharged from the body the abortion bacilli no longer flourfsh, al- 

 though the infection may continue as a chronic uterine inflammation 

 for a long time. The general health is only slightly disturbed. At the 

 next pregnancy the disease is practically certain to reappear, and pos- 

 sibly again also at the succeeding one. After two or three abortions the 

 animals appear to have acquired an immunity to the infection, and may 

 sometimes breed normally thereafter, although some animals are per- 

 manently sterile after a few attacks of the disease. 



The organisms escape from the diseased animal in the products of 

 conception at the time of the abortion, and in the chronic uterine dis- 

 charge which may continue for a long time afterward. The disease may 

 be conveyed to other animals by contact with this material and by 

 eating grass or other feed soiled with it. Doubtless the male is an im- 

 portant factor, possibly the most important factor, in transmitting the 

 disease, although Jio serious inflammation is produced in him. 



