342 SPECIFIC MICRO-ORGANISMS 



Bacillus (Bacterium) Acne. This minute non-motile organ- 

 ism, first described by Gilchrist, is constantly present in the pap- 

 ules and pustules of the common skin affection, acne vulgaris. 

 Cultures are most readily obtained by expressing, with careful 

 asepsis, some of the cheesy pus from a recent papule and mixing 

 it with 2 c.c. of ascitic fluid in a test-tube. Dilutions from this 

 are made to similar amounts of ascitic fluid in series (about five 

 tubes in all). To each tube are then added 8 c.c. of melted 

 glucose agar cooled to 50 C., the contents of each tube mixed 

 without introducing air bubbles and then quickly solidified by 

 immersion in cold water. The colonies of B. acne develop at 

 37 C. after five to ten days, beginning about 8 mm. beneath 

 the surface, and they grow best in a narrow zone about 5 mm. in 

 depth. The colonies attain a large size (3 mm.) and an abundant 

 supply of bacillary substance for preparation of vaccine may be 

 obtained by thrusting a sterile glass capillary into such a colony. 

 In its behavior to oxygen when first isolated the organism exhibits 

 the same peculiarity as the bacillus mentioned in the preceding 

 paragraph. 



Bacillus (Bacterium) Bifidus. Tissier in 1898 showed that 

 the Gram-positive bacillus predominant in the stools of healthy 

 nurslings is not a form of B. coll as had been supposed since the 

 investigations of Escherich (1886) but is an entirely different 

 organism. He obtained cultures by making a series of dilutions 

 (five to ten tubes) in tall tubes of glucose agar by the method of 

 Veillon (see page 112). The colonies develop best about i to 2 

 cm. beneath the surface after three to eight days at 37 C. In 

 these colonies many of the bacilli show dichotomous branching. 

 Bifid forms are also sometimes seen in stools and in mixed cul- 

 tures in broth. The organism produces a strong acid reaction 

 and the cultures soon die out. The bifid forms are doubtless 

 involutions due to presence of unfavorable amounts of acid. 



Bacillus (Bacterium) Bulgaricus. This organism is a rather 

 large rod i by 6ju approximately. It occurs in milk and milk 

 products and is especially abundant in milk fermented at 40 C. 



