CLASSIFICATION 431 



The mammalian bacilli generally produce no recognizable lesions in fowls or pigeons, 

 but occasionally a local abscess forms, which contains a few bacilli. Avian bacilli 

 are pathogenic to rabbits if inoculated intravenously, giving rise to the Yersin 

 type of disease (see p. 425). Grifl&th used to inject 0-01 mgm. intravenously into 

 rabbits and 10 mgm. intramuscularly into hens. Sometimes, however, avian 

 strains are encountered, particularly from pigs, that are pathogenic to fowls but 

 not to rabbits. 



Lesions caused by the Injection of Dead Tubercle Bacilli. — The injection into 

 animals of dead tubercle bacilli, preferably killed by heat, gives rise to lesions 

 of varying degrees of severity. Subcutaneous injection provokes merely a local 

 abscess, but after intravenous injection the dead bacilli are deposited in the viscera, 

 where they give rise to small follicular lesions closely resembling true tubercles, 

 and sometimes vmdergoing caseation. This disease is known as Necro -tuberculosis 

 (Miller 1905). Apparently the dead bacilli are attacked and broken down by the 

 cells of the body and their intracellular toxins liberated ; these toxins then act on 

 the tissues, and give rise to the characteristic lesions of tuberculosis. For the 

 production of necro-tuberculosis, virulent bacilli are not essential ; we have pro- 

 duced lesions in rabbits by the intravenous injection of dead avirulent bacilli, such 

 as Calmette's B.C.G. strain. 



Classification. — We have already indicated that the acid-fast bacilli may be 

 divided into six types — human, bovine, murine, avian, and cold-blooded tubercle 

 bacilli, and the saprophytic acid-fast bacilli. The distinction between the types 

 rests chiefly on cultural appearances and pathogenicity, aided when necessary by 

 serological reactions. These types are remarkably constant ; so far as we are 

 aware, no clear evidence has ever been produced to prove that one type may change 

 into another. Numerous experiments have been made by different methods to 

 bring this about, but no one has yet succeeded in doing so. 



Nevertheless, the division of the mammalian tubercle bacilli is not always 

 clearly defined. From time to time aberrant strains are encountered, which 

 depart from the standard type either in cultural behaviour, in pathogenicity, or 

 in both. The most fruitful source of these aberrant types is lupus ; thus from 

 140 cases of lupus examined by A. S. Griffith (1924), no fewer than 99 yielded 

 strains of aberrant type. Apparently, when growing in the skin, tubercle bacilli 

 are liable to undergo a modification in virulence, so that both human and bovine 

 types become less pathogenic for experimental animals. Aberrant types are 

 encountered in other lesions, though much less frequently ; thus Griffith (1916) 

 found 4 aberrant strains amongst a total of 212 strains isolated from sputum, 

 and 5 amongst 141 strains isolated from bone and joint disease (1916-17) ; East- 

 wood and F. Griffith (1916) likewise isolated 10 aberrant out of a total of 261 strains 

 from cases of bone and joint disease. Aberrant strains have occasionally been 

 found in animals, especially horses (A. S. Griffith 1924, Stableforth 1929). 



The mammalian bacilli may be subdivided as follows (Table 28, p. 432). 



Of these various types the attenuated eugonic human and the attenuated 

 dysgonic bovine are the ones usually found in lupus ; the attenuated dysgonic 

 human and attenuated eugonic bovine are rare, and have been met with in lupus 

 only. The dysgonic human type was the type isolated from sputum and from bone 

 and joint disease, in the cases already referred to. On serum and glycerine serum 

 it grows luxuriantly with the production of yellow pigment. But on glycerine agar 

 and glycerine potato growth is very slow ; an effuse grey glazed layer of growth 



