ABORTION BACILLUS GROUP 



343 



is present per every 240 c.c. of space. It has been found experi- 

 mentally that this will diminish the oxygen pressure to a point 

 where the Bacillus abortus will develop. After three days the 

 plates are examined and search made for the B. abortus in the 

 spaces between other colonies on the original plates. This same 

 device, of reducing oxygen pressure by means of cultures of Bacil- 

 lus subtilis, may be used in the study of growth-characters on 

 other media. The organism will grow in agar without addition 

 of serum, particularly at the surface, but the addition of serum is 

 decidedly beneficial. The colonies develop at the surface in about 

 three days at 37 as small, usually discrete, transparent dots. In 

 shake cultures in serum agar they appear in about four days in 

 a well-defined stratum about 10 to 20 mm. below the surface. 

 The individual colonies may reach a 

 diameter of 1 mm. when well separated 

 from each other. Growth in gelatin 

 at room-temperature is slow. Bouil- 

 lon cultures show development some 

 millimeters below the surface, the 

 medium above this remaining clear. 

 Milk is not coagulated. Little or no 

 growth takes place on potato^^- 



Physiology. The optimum growth 

 temperature is 37, although the organ- 

 ism is found to multiply slowly at 

 room-temperature. The relationship 

 to oxygen, which has already been 



discussed, classifies the B. abortus as a micro-aerophile rather 

 than a strict anaerobe. Strangely enough, Bang reports that the 

 organism will also grow in an atmosphere of pure oxygen; two 

 oxygen optima are, therefore, evident. It is relatively resistant 

 to desiccation. It will remain alive for months in a retained 

 mummied fetus, and for a year or more in a culture-medium. 

 Acids and gas are not produced from carbohydrates. 



Pathogenesis. Experimental Evidence. Bang demonstrated 

 the etiologic relationship of the organism to the disease by intra- 

 venous injection, and by injection into the vagina and uterus of 

 pregnant cows. Preisz did not succeed in transmitting the disease 



Fig. 142. Bacillus abor- 

 tus. Culture in serum agar 

 showing the definite stratum 

 in which the colonies develop 



(Xowak). 



