420 MYCOBACTERIUM 



of Ishimori, who found that the human preferred a more alkaline reaction than the 

 bovine bacillus. 



The optimum temperature for growth of the human, bovine, murine, and, 

 generally the saprophytic acid-fast bacilli, is 37° C. ; for the avian 40° C, and 

 for the cold-blooded bacillus 25° C. The human, bovine, and avian types do 

 not grow below 30° C, the cold-blooded and saprophytic acid -fast types grow 

 freely at 20° C. Many saprophytic acid-fast bacilli grow at 45° C, and a few 

 at 55° C. 



The tubercle bacillus is an aerobe ; it will not grow under strictly anaerobic 

 conditions. The optimum partial pressure of oxygen is said to be 40-50 per cent, 

 for the human type (Novy and Soule 1925) and 60-70 per cent, for the avian and 

 saprophytic acid-fast types (Uga 1935). Novy and Soule in their very careful 

 study of the respiration of the tubercle bacillus found that CO 2 had little effect on 

 growth, and no inhibition occurred till a partial pressure of 60 per cent, was reached. 

 Subsequent observations, however, by Rockwell and Highberger (1926) and others 

 have shown that CO 2 is beneficial for growth. For optimal development it is 

 desirable to incubate cultures in a high partial pressure of oxygen and about 10 per 

 cent. CO 2- A few measurements have been made on the oxygen uptake of the 

 bacilli (Dieckmann and Menzel 1932), and on the oxidation-reduction potential 

 established in phosphate buffer solutions (Aksianzew 1933). 



Moisture is an essential requirement of the tubercle bacillus in vitro. For good 

 growth to occur, plenty of condensation water— suppUed best by passing steam into 

 the tube before inoculation— and an abundance of air are essential. Growth does 

 occur in sealed tubes provided plenty of moisture is present, but it ceases after 

 3 or 4 weeks. 



The effect of glycerive on the growth of the tubercle bacillus has been the subject 

 of much controversy. Nocard and Roux in 1887, working apparently with an 

 avian strain, were the first to notice the beneficial action of this substance. Since 

 then it has been found that the addition of glycerine, generally in a concentration 

 of 5 per cent., greatly increases the growth of all acid-fast bacilU with the exception 

 of the murine, and to some extent the bovine tubercle bacillus. On this organism 

 glycerine is not without effect ; for it will enable it to grow — though very poorly 

 — on agar, potato, or broth, on which no growth otherwise occurs. But the 

 favourable action of glycerine on the bovine bacillus is not to be compared with 

 that on other types ; the addition of glycerine, for example, to serum or egg 

 medium, makes no difference to the growth of the bovine bacillus, whereas it 

 greatly increases the growth of all the other acid-fast bacilli. 



The difference in the effect of glycerine on growth was made use of by Smith (1904-05) 

 in the elaboration of a test for distinguishing between the human and bovine types. He 

 found that if bovine tubercle bacilh were grown in glycerine broth, which had an acid 

 reaction to phenol-phthalein, the acidity gradually decreased, till after full growth had 

 occurred the reaction was about neutral ; in cultures of human bacUh, on the other hand, 

 after an initial production of alkaU, the reaction gradually became acid agam. That 

 is to say, the final reaction of a bovine cultvu-e was about neutral, of a human culture 

 decidedly acid. This difiference in the reaction curve of the two types of mammahan 

 baciUi has been investigated by numerous workers, some of whom have confirmed, and 

 some of whom have not confirmed. Smith's observations. Undoubtedly one of the reasons 

 for this discrepancy is that most of the work was done before the days of accurate deter- 

 mination of acidity by measurement of the H-ion concentration was possible. Smith's 

 view, put briefly, was that the human bacillus was able to utUize glycerine with the con- 



