434 M YCOBAGTERI UM 



5 per cent. Glycerine Agar. — 4 weeks, 37° C. Thick, raised, confluent, cream-coloured growth 

 with a nodular or wrinkled surface. 



5 per cent. Glycerine Potato. — 4 weeks, 37° C. Thick, raised, confluent growth, creamy or 

 yellow in colour, with a wrinkled, nodular, or warty surface. 



5 per cent. Glycerine Broth. — 4 weeks, 37° C. Greyish-white surface pellicle, often irregularly 

 thickened in places. On further incubation the pelhcle increases in thickness, 

 develops a deeply wrinkled surface, and spreads for about J inch up the sides of 

 the flask. No turbidity, but often a sUght granular deposit. 



Plain Agar or Broth. — No growth, as a rule. 



Resistance. — Cultures live for 4 to 8 weeks as a rule, but may remain viable for a year. 

 Bacilli are killed by moist heat at 60° C. in 15 to 20 minutes. In excised tissues, 

 kept at 37° C, they die in about a week. In dried sputum most of the bacilli die 

 in a few days. Are fairly susceptible to sunlight and ultra-violet light. Moderately 

 resistant to chemical disinfectants ; in sputum may survive exposure to 5 per 

 cent, phenol or antiformin for 24 hours. 



Metabolism.— Growth, occurs between pH 4-5 and 8-0 ; optimum pH is 70-7-6. Optimum 

 temperature 37° C. ; very little growth, if any, below 30° C. Growth occurs best 

 in an atmosphere of 40-50 per cent. Og ; no growth under strictly anaerobic con- 

 ditions. Growth is improved by addition of glycerine and of dead acid-fast bacilli 

 to the medium ; and is said to be improved by substances rich in Vitamin B, and 

 by very small quantities of iron salts. Golden-yellow pigment produced on 

 glycerinated ox serum. 



Biochemical. — Very little known about biochemical properties. Evidence that the baciUi 

 can produce acid from glucose, maltose, lactose, sucrose, glycerol and trehalose. 



Antigenic Structure. — By agglutination, absorption of agglutinins, and complement fixa- 

 tion the human bacilU are shown to form a homogeneous group indistinguish- 

 able from bovine tubercle baciUi, but easily distinguishable from avian, cold- 

 blooded, and saprophytic acid-fast baciUi. 



Pathogenicity. — Produces tuberculosis in man, pigs, monkeys, dogs, and parrots. Experi- 

 mentally, it is highly pathogenic for the guinea-pig, but not for the rabbit, 

 cat, goat, or ox. A minute quantity injected subcutaneously into a guinea- 

 pig's thigh causes death in 6 to 12 weeks. P.M. local caseous abscess ; enlarge- 

 ment and caseation of the inguinal, sublumbar, portal, axillary, and bronchial 

 glands ; enlargement of the spleen with production of irregular yellowish areas 

 of necrosis ; enlargement of the liver with production of smaller, irregular, greenish- 

 yellow areas of necrosis ; few rounded tubercles in the lungs. Tubercle bacilli 

 are numerous in the local lesion and the inguinal glands ; more scanty elsewhere. 



The characters of the different types of tubercle bacilli, including the saprophytic 

 acid-fast bacilli, are summarized in the table on pp. 435-7 (Table 29). 



The Leprosy Bacillus 



The causative organism of leprosy, which was one of the first micro-organisms 

 shown to be pathogenic to man, was discovered by Hansen in 1868, though his 

 published account did not appear till 1874. He observed it in the tissues of lepers, 

 where it occurs in large numbers in the granulation tissue cells. The bacilli vary 

 in size and shape ; they may be straight or slightly curved, 1-8 fx in length, with 

 parallel sides and rounded ends, arranged chiefly in clumps or bundles, and staining 

 evenly ; or they may resemble diphtheroids and show granular staining, confined 

 to the poles or distributed throughout their length. They are not easily stained 

 without a mordant ; they are Gram-positive and strongly acid-fast. They are 

 non-motile and non-sporing. 



Though the leprosy bacillus was one of the first of the pathogenic organisms to 



