METABOLISM 421 



sequent production of acid, whereas the bovine bacillus was unable to use it, and so caused 

 an increased hydrolysis of protein and an alkaUne reaction. Whether Smith's view is 

 correct or not, it is stiU impossible to say. The reaction curve of broth cultures is deter- 

 mined by so many factors, such as the production of NH3, CO2, amino-acids, and other 

 substances, some of which are volatile, and some of which are not, that it is almost impos- 

 sible to determine whether the production of acid is due to disintegration of the glycerine 

 by the baciUi, or to hydrolysis of the protein material. Harden (1913), who made a 

 special investigation of this subject, failed to obtain evidence of any definite distinction 

 in biochemical behaviour between the human and the bovine types. Kendall, Day and 

 Walker (1920), who have examined the question more recently, conclude that glycerine 

 probably exerts a sparing action on the protein constituents of the medium in cultures 

 of the human, but not in cultures of the bovine type ; but, as noted elsewhere (p. 57), 

 the existence of this protein-sparing effect is very doubtful. It is not possible to discuss 

 this problem more fully (for a fuU discussion of the work up to 1917 see Cobbett 1917) ; 

 but we may conclude that as a practical means of differentiating the human from the 

 bovine bacillus, determination of the glycerine-broth reaction curve is too complex for 

 routine use. 



Glucose seems to act in much the same way as glycerol (see KaufTmaon 1932). 

 The growth of tubercle bacilli is likewise improved by the addition of extracts of 

 acid-fast bacilli to the medium ; certain organisms, such as Johne's bacillus, will 

 not grow at all unless such an extract is added (see p. 441). The tubercle bacillus 

 has been grown in a number of synthetic media (see Wells and Long 1932) ; its 

 growth is said to be increased by the addition of substances containing vitamin B, 

 siich as yeast, and of orange, tomato, or cabbage juice (Uyei 1927) (but see p. 66). 

 Schmidt (1925) found 0-01 per cent, of iron chloride to favour growth, but Da vies 

 (1937) had the opposite experience. The effect of blood seems to be complex ; 

 tubercle bacilli grow well in liquid blood, particularly if lysed by saponin (Pryce 

 1941), but are generally inhibited by blood on the surface of a solid medium (Evans 

 and Hanks 1939). Old potatoes that blacken on standing are more favourable 

 for growth than new ones that do not (McCarter and Tatum 1937). Saprophytic 

 acid-fast bacilli are said to grow in a simple solution of inorganic salts containing 

 neither carbon nor nitrogen (Bruner 1934, Gordon and Hagan 1937). There is 

 evidence that tubercle bacilli can oxidize certain fats, such as those of olive oil 

 and butter (Sedyeh and Seliber 1927). 



Pigment production is very variable. On deeply coloured batches of ox serum 

 the human bacillus often forms a rich yellow or orange-yellow growth. A pink 

 coloration on glycerol egg medium is not uncommon with avian strains, and accord- 

 ing to Blacklock (1932) is sometimes given by rapidly growing bovine strains. 

 Cold-blooded bacilli generally give colourless growths. On the other hand, the 

 growth of nearly all the saprophytic acid-fast bacilli is accompanied by the produc- 

 tion of a yellow, pink, orange, or brick-red pigment. On Sauton's medium a green 

 coloration is not infrequently observed with cultures of mycobacteria ; its intensity 

 varies from strain to strain (Lange 1932, de Grolier 1933, Kraus and Koref 1933). 

 Pigment formation seems to depend on a number of different environmental factors, 

 particularly the composition of the medium and the oxygen supply. Keed and Rice 

 (1929) found that the addition of iron favoured its formation. On a glycerol agar 

 medium containing 0-02 per cent, of ferric citrate, human, bovine, and avian types 

 of tubercle bacilli, and saprophytic acid-fast bacilli, all formed pigment of varying 

 depth, whereas on the same medium without iron many strains formed no pigment 

 at all. Pigment production is not well developed at 37° C. ; it is best seen in 



