MORPHOLOGY AND STAINING 405 



timothy-grass bacillus ; his second bacillus was isolated in 1899 from the dust 

 of some plant material used as fodder ; (iii) the Mist bacillus or Myco. stercoris ; 

 this was isolated by Moeller in 1901 from a dung-heap, and later from the faeces 

 of cows, donkeys, and other herbivora ; it owes its name to the German term 

 for manure (Mist) ; (iv) the Smegma bacillus, Myco. smegmatis ; this was first 

 described by Alvarez and Tavel in 1885, but was not obtained in pure culture 

 till 1897, when Laser (1897) and Czaplewski (1897) cultivated it independently. 

 This organism is present in varying numbers in smegma of both males and females ; 

 it has been found in the smegma of dogs (Pellegrino 1906). 



Finally, in 1937 Wells isolated an acid-fast bacillus from voles {Microtus agrestis) 

 suffering from natural tuberculosis. This organism differs in certain respects 

 from the other mammalian types, and is probably best referred to as the murine 

 type of tubercle bacillus or Myco. muris. 



We shall describe the tubercle and saprophytic acid-fast bacilli together in 

 the body of this chapter, but shall reserve the leprosy, rat leprosy, and Johne's 

 bacillus for a separate description at the end. 



Habitat. — The tubercle bacilli are essentially pathogenic ; so far as we know 

 they do not multiply naturally outside the animal body. The human, bovine, 

 and murine bacilli give rise to mammalian tuberculosis (see Chapter 59). The 

 avian type is found chiefly in birds, though it often infects pigs and occasionally 

 cattle. It is sometimes present in hens' eggs (see Gloyne 1933). The cold-blooded 

 type is responsible for disease in cold-blooded animals and fish. The saprophytic 

 acid-fast bacilli are found in such diverse surroundings as butter, milk, smegma, 

 grass, manure, and faeces ; they are also widely distributed in dust and water. 

 The presence of metal seems to favour their growth, and they can almost invari- 

 ably be found in scrapings from metal cold-water taps (Brem 1909, Beitzke 1910) 

 and metal wind instruments (Jacobitz and Kayser 1910). They have been reported 

 in cultures made from a gangrenous lung (Rabinowitsch 1900), from human faeces 

 (Mironescu 1901), from the tonsils (Marzinowsky 1900, Beck 1905), from the nasal 

 secretion (Karlinski 1901, Marchoux and Halphen 1912), from the intestinal contents 

 of insects (Pellegrino 1906), from cow's milk (Albiston 1930), from a pleural exudate 

 (Beaven and Bayne-Jones 1931), from pus (Bruynoghe and Adant 1933), from 

 sputum (Cummins and Williams 1933), and from blood (Tiedemann 1931, Schwa- 

 bacher 1933a). In view, however, of the frequency of acid-fast bacilli in dust, it 

 seems probable that some of these organisms gained access to the cultures by air 

 contamination and were not necessarily present in the material from which they 

 were apparently derived. The leprosy bacillus is a specific parasite of man, and 

 the rat leprosy bacillus of rats. Johne's bacillus infects cattle, and to a less extent 

 sheep, in both of which it causes a chronic enteritis. 



Morphology and Staining.- — The acid-fast bacilli are rod-shaped organisms 

 straight or slightly curved, with more or less parallel sides and rounded ends, 

 they are arranged either singly, in small groups or bundles, or in groups of three 

 or four with the individual bacilli lying at acute angles to each other, resembling 

 diphtheria bacilli. Their size varies considerably according to the medium on 

 which they are grown. In the animal body they are generally longer and thinner 

 than in culture. Their length is 1-4 fi, but occasional forms as long as 8 /^ are 

 seen ; in breadth they vary from about 0-3-0-6 fx. Long filamentous acid-fast 

 bacilli have been described, but it is probable that these belong to the Actino- 

 myces group (see Chapter 14). Numerous authors, however, have stated that 



