428 MYCOBACTERIUM 



cutaneous, intraperitoneal, or intravenous injection of avian bacilli into fowls or pigeons 

 gives rise to fatal tuberculosis. At necropsy, the main lesions are found in the liver and 

 spleen, which contain rather hard caseous tubercles well differentiated from the surrounding 

 tissue. After feeding experiments, tubercles are often seen projecting through the peri- 

 toneal covering of the intestine. 



Cold-blooded Animals.^ — The cold-blooded type of tubercle bacillus is unable to set 

 up progressive disease in mammals or probably birds ; after subcutaneous injection of large 

 doses a local lesion may result, but the disease does not spread. Frogs, turtles, lizards, 

 snakes, fish and other cold-blooded animals are susceptible to experimental inoculation with 

 the cold-blooded type, and are generally regarded as insusceptible to the mammalian 

 and avian types. Griffith (1941c), however, states that the water or grass-snake {Trepi- 

 donotus natrix) is highly susceptible to experimental infection with the avian type. He 

 (1941rf) has also found that mammalian and avian bacilli, if inoculated into the dorsal 

 sac of a toad, multiply slowly in the hver and may be recovered 1, 2, or 3 years later. 

 Subcutaneous or intraperitoneal inoculation with cold-blooded bacilli gives rise to lesions 

 that are often widely distributed throughout the viscera. Their nature depends on the 

 site of inoculation and the time of survival. Soft, nodular lesions in the liver or lungs, 

 filled with creamy or caseous material, are not uncommon. Sometimes the liver is studded 

 with little greyish-white granules, almost confluent (see Ledoux-Lebard 1900, Friedmaim 

 1903, Kiister 1905). Whether cold-blooded bacilli are pathogenic for birds is not clear. 

 Aronson (1926) states that he isolated a cold-blooded bacillus from certain salt-water 

 fish — a sergeant-major {Abudefduf mauritii), three croakers (Micropogon undulatus), and 

 two sea-bass {Centropristes striatus) — which proved pathogenic for pigeons. 



Developing Chick embryo. — A few observations have been made on the growth of tubercle 

 bacilh on the chorio-allantoic membrane of the developing chick embryo. According 

 to Fite and Olson (1944), the lesions produced under these conditions by the human type 

 of bacillus differ from those caused by the bovine and avian types. Though the method 

 may be of differential value, it does not appear to be suited for estimating the virulence of 

 strains to their natural animal host. 



Table 27 modified from Cobbett (1932), summarizes the reaction of different 

 animals to the four main types of tubercle bacilli. 



The saprophytic acid-fast bacilli are unable to set up a progressive infection in 

 mammals or birds. Nevertheless, when inj ected intraperitoneally in fairly large doses, 

 especially together with some fatty protective substance such as butter, they may 

 give rise to extensive lesions closely simulating those of true tuberculosis (see 

 Rabinowitsch 1897, Grassberger 1899, Hagan and Levine 1932). This appears to 

 result from the dissemination of the bacilli in the tissues by the lymph stream and 

 leucocytes, and the subsequent focal reaction of the tissues around them. True 

 nodule formation and caseation may occur, and acid-fast bacilli are found micro- 

 scopically in the lesions. After subcutaneous or intramuscular inoculation the 

 lesions are usually confined to the local site and the regional lymphatic glands. 

 The disease may be distinguished, however, from tuberculosis by culture and 

 by further inoculation. Cultures made from the lesions on to glycerine agar 

 will reveal a growth of saprophytic acid-fast bacilli in 2 or 3 days ; while further 

 inoculation into a guinea-pig, using a saline suspension of a small portion of one 

 of the lesions, will prove innocuous. Histologically, the lesions caused by the 

 saprophytic acid-fast bacilli show more exudation than proliferation ; there is less 

 tendency to caseation and more to suppuration ; polymorphonuclear are commoner 

 than epithelioid cells ; and typical giant cells with peripheral nuclei are 

 rare (Rabinowitsch 1897). Saprophytic acid-fast bacilli injected intravenously 



