cal with this species, although it is more difficult to cultivate (Dunkin and Balfour- Jones, Jour. Comp. Path., 48, 1935, 236). Source: Isolated from the intestinal mu- cous membrane of cattle suffering from chronic diarrhoea. Apparently an obligate parasite. Habitat: The cause of Johne's disease, a chronic diarrhea in cattle. Found in the in- testinal mucosa. 13. Mycobacterium leprae (Hansen, 1874) Lehmann and Neumann, 1896. (Bacil- lus leprae Hansen, Norsk. Mag. Laegevi- densk., 9, 1874, 1; also see Arch. f. path. Anat. u. Physiol., 79, 1879, 32; Nord. Med. Ark., 12, 1880, 1; and Quart. Jour. Micro. Sci., £0, 1880, 92; Lehmann and Neumann, Bakt. Diag., 1 Aufl., 2, 1896, 372). lep'rae. Gr. noun lepi-a leprosy; M.L. gen. noun leprae of leprosy. Common name: Leprosy bacillus or Han- sen's bacillus. Though not yet cultivated in vitro, these bacilli were the first to be recognized as a cause of human disease (Hansen, op. cit., 1874). The bacilli occur in enormous num- bers in lepromatous (nodular) cases of leprosy (Hansen's disease) and very sparsely in the tuberculoid or neural forms. Bacteriological identification depends on: (a) acid-fast staining and (b) failure of the organism to multiply in bacteriological media or in laboratory animals. Heated sus- pensions of the bacilli (obtained from nodules) produce a positive lepromin reac- tion in 75 to 97 per cent of normal persons and of tuberculoid cases of leprosy but usually produce no reaction in lepromatous individuals (Mitsuda: See Hayashi, Int. Jour. Leprosy, 1, 1933, 31-38). The failure of lepromatous persons to respond to injected leprosy bacilli constitutes a criterion for testing the validity of the acid-fast micro- organisms which can at times be recovered from leprous tissues by inoculation of bac- teriological media. Many organisms have been isolated from leprous tissues, some of which are acid-fast and which have been styled Mycobacterium leprae. The strains which have been ade- quately studied have proven to fall into the saprophytic groups. Hanks (Int. Jour. Lep- rosy, 9, 1941, 275) found that acid-fast cultures of this type were recoverable only from lesions located proximally with respect to open ulcers in the skin. Description of organisms seen in leprosy tissue from Hansen {op. cit., 1874, 1) and Topley and Wilson (Princip. Bact. and Im- mun.. London, 2nd ed., 1936, 316). Rods, 0.3 to 0.5 by 1.0 to 8.0 microns, with parallel sides and rounded ends, stain- ing evenly or at times beaded. When numer^ ous, as from lepromatous cases, they are generally arranged in clumps, rounded masses or in groups of bacilli side by side. Strongly acid-fast. Gram-positive. Pathogenicity: The communicability of leprosy from man to man is accepted (Rogers and Muir, Leprosy, 2nd ed., Balti- more, 1940, 260 pp.). Experimental trans- mission to humans or to animals has not been successful. Source: Found in human leprous lesions. In the lepromatous form of the disease, bacilli are so abundant as to produce stuffed-cell granulomas; in the tuberculoid and neural lesions they are rare. Habitat: Obligate parasite in man. Con- fined largely to the skin (especially to convex and exposed surfaces) , testes and to peripheral nerves. Probably do not grow in the internal organs. 14. Mycobacterium lepraemurium Marchoux and Sorel, 1912. (Bacillus der Rattenlepra, Stefansky, Cent. f. Bakt., I Abt., Orig., 33, 1903, 481; Mycobacterium leprae murium (sic) Marchoux and Sorel, Ann. Inst. Past., 26, 1912, 700.) lep.rae.mu'ri.um. Gr. noun lepra leprosy; L. noun mus the mouse; L. gen. noun muris of the mouse; M.L. noun lepramuris leprosy of the mouse; M.L. gen. pi. noun lepraemu- rium of leprosy of mice. Common name: Rat leprosy bacillus. Rods, 3 to 5 microns in length, with slightly rounded ends. When stained, the cells often show an irregular appearance. Strongly acid-fast. Gram-positive. Like the human leprosy bacillus, this or- ganism has not been cultivated in vitro, but it can be passed experimentally through rats, mice and hamsters. Distinctive characters: The heat-killed
