METABOLISM 771 



minutes. Agar plate cultures exposed to sunlight are sterilized in 3 or 4 hours 

 (Ogata 1897). Dried on threads and kept at room temperature in a desiccator 

 the bacilli survive for not more than a few days. In bubo juice, dried on a cover 

 slip, Past, pestis dies in under 4 days (Kitasato 1894) ; but in dry flea faeces kept 

 at room temperature (66° F.) it may survive for 5 weeks (Eskey and Haas 1940). 

 The blood of animals dying from haemorrhagic septicaemia remains virulent in the 

 dried state for about 3 weeks ; blood which is allowed to putrefy in a glass tube 

 may remain virulent for 100 days (Ostertag 1908). Bacilli in cultures or infected 

 organs, kept in the ice-chest, may survive for months. According to Francis 

 (1932), Past, pestis, in an infected guinea-pig's spleen kept in pure neutral glycerol 

 at — 15° C, may retain its virulence for years. 



Metabolism. — The bacilli have a wide range of growth. Past, pestis and Past, 

 pseudotuberculosis can grow to some extent at very low temperatures — according to 

 Tumansky and his colleagues (1935) even at 0° C. Their upper limit of growth is 

 about 43° C. Different observers disagree about their optimum temperature for 

 growth, but 30° C. is generally considered to be the most favourable. Growth, 

 however, at both 24° C. and 37° C. is often nearly as good as at 30° C. According 

 to Sokhey and Habbu (1943), Past, pestis grows in nutrient broth between — 2° 

 and -{- 45° C. ; at 27 to 28° C. — its optimum temperature — growth is five times 

 as rapid as at 37° C. Pasteurella septica has a rather narrower range of growth, 

 and develops best at 37° C. 



All the members are aerobes and facultative anaerobes. Working with Past, 

 lepiseptica, Webster (1924«, 1925) and Webster and Baudisch (1925) found that 

 the D or smooth variant would not grow in plain broth unless large numbers of 

 organisms were introduced — about 100,000 per ml. ; whereas the G or rough variant 

 grew if only a few organisms were introduced. But if a trace of rabbit blood, or 

 an iron compound with strongly catalytic properties, was added to the medium, or 

 the partial pressure of oxygen was lowered mechanically, growth of the D variant 

 occurred with the smallest inoculum. Schiitze and Hassanein (1929) made similar 

 observations on Past, pestis. They found that the difficulty of obtaining growth 

 from small inocula on agar plates-could be overcome by the addition of a small 

 amount of blood or of 0-025 per cent, sodium sulphite to the medium, or by incuba- 

 tion under anaerobic conditions. Their conclusion that the organisms were sen- 

 sitive to oxygen was confirmed by Wright (1934), who found that plague bacilli were 

 destroyed fairly rapidly on the surface of agar plates if exposed at 37° C. to a 

 partial pressure of oxygen exceeding 1 per cent. Aerobic surface cultivation was, 

 however, successful if 0-1 percent, of blood, 10 per cent, of serum, or 0-05 per cent, 

 of sodium sulphite was added to the agar. Under these conditions growth was more 

 profuse aerobically than anaerobically. For the growth of Past, pestis Kao (1939) 

 found that three amino-acids, proline, phenylalanine, and cystine, were required ; 

 glucose and lactate were the two best sources of carbon and energy with which 

 to supplement media. Growth was stimulated by glycine, haematin, cozymase, 

 thiamin and nicotinic acid ; haematin appeared to be essential for the aerobic 

 growth of plague bacilli when these were present in only small numbers. 



On horse blood agar plates there is no haemolysis around the colonies, but the 

 whole plate is slightly cleared and browned. When a suspension of bacilli is incu- 

 bated with sheep's red cells there is again no haemolysis, but the oxyhaemoglobin 

 is reduced to haemoglobin. In this respect all members behave alike. 



No true exotoxin is formed (Hadley 1918). Old broth cultures are, however, 



