Cultivation 585 



appears uniformly colored, being darker at the ends than 

 at the center, so as to resemble a dumb-bell or diplococcus. 

 The bacilli sometimes appears vacuolated, and nearly all 

 cultures show a variety of involution forms. Kitasato has 

 compared the general appearance of the bacillus to that of 

 chicken-cholera. 



Involution forms on partly desiccated agar-agar not 

 containing glycerin are said by Haffkine to be characteris- 

 tic. The microbes swell and form large, round, oval, pea- 

 shaped, spindle-shaped or biscuit-like bodies which may at- 

 tain twenty times the normal size, and gradually lose the 



Fig. 203. Bacilli of plague and phagocytes, from human lymphatic 

 gland. X 800 (Aoyama). 



ability to take the stain. Such involution forms are not 

 seen in liquid culture. 



Cultivation. Pure cultures may be from the blood or 

 from the softened contents of the buboes, and develop well 

 upon artificial media. The optimum temperature is about 

 30 C. The extremes at which growth occurs are 20 and 

 38 C. 



Bouillon. In bouillon a diffuse cloudiness was ob- 

 served by Kitasato, though Yersin observed that the cul- 

 tures resembled erysipelas cocci, and contained zooglea 

 attached to the sides and at the bottom of the tube of 

 nearly clear fluid. 



