METABOLISM 645 



rest occurs regularly, a fresh ring of growth being formed about every 4 hours till 

 the plate is covered. It is due to this periodic extension that the surface of the 

 growth appears rippled or contoured (see Kuss-Miinzer (1935)). 



Though the property of swarming is generally considered to be peculiar among 

 aerobic bacteria to the Proteus group, it has been pointed out by Kauss (1936) that 

 strains of Morgan's (1906) bacillus, which have not hitherto been included in 

 this group, also exhibit the ability to swarm under appropriate conditions. On 

 ordinary agar at 37° C. this organism forms circumscribed colonies, but on solid media 

 containing only 1 per cent, agar incubated at 20-28° C, characteristic swarming 

 occurs. Variant forms are described having a less marked power to spread, and 

 these give rise to colonies distinguished by varying degrees of peripheral spread as 

 well as by their structural appearance. 



In broth Proteus gives rise to a uniform turbidity accompanied by a slight to 

 moderate powdery deposit and a faint ammoniacal smell. Cantu (1911) states 

 that a surface pellicle is never formed, while Wenner and Rettger (1919) and Yacob 

 (1932) say that a thin fragile pellicle may develop in older cultures. Gelatin plate 

 colonies are very characteristic (Cantu 1911). 



Resistance. — Few observations appear to have been made on the resistance of 

 Proteus bacilli. Our own limited experience has shown that they are readily 

 destroyed by heat and disinfectants. Exposure to moist heat at 60° C. for 1 hour 

 is sufficient to sterilize a broth culture. A 1 per cent, phenol solution, inoculated 

 with one million organisms per ml., is found to be sterile within 30 minutes. 



Metabolism. — The members of this group are aerobes and facultative anaerobes. 

 Growth under strict anaerobic conditions is very poor, and certain enzymic activi- 

 ties may be suppressed. The optimum temperature for growth is about 34-37° C, 

 though rapid multiplication occurs above 20° C. The limits of growth are between 

 about 10° C. and 43° C. 



Reports on the heemolytic activity of Proteus are discrepant. Wenner and 

 Rettger (1919) obtained uniformly negative, and Norton, Verder, and Ridgway 

 (1928) uniformly positive results. In neither of these reports is the type of blood 

 mentioned. Taylor (1928), using human blood, observed haemolysis regularly 

 within 24 hours in 1 per cent, blood broth, but not on 10 per cent, blood agar plates. 

 Yacob (1932) used 5 per cent, rabbit blood agar plates, and found that all strains 

 produced /^-haemolysis in 24-48 hours. As with many other organisms, it seems 

 probable that the nature of the blood is an important factor in determining the 

 result. 



The main features that distinguish Proteus bacilli from other Gram-negative 

 gelatin-liquefying rods are the production of HoS and the active decomposition of 

 urea (Moltke 1927). According to Wolf (1918-19), urea is broken down readily, 

 as much as 45 per cent, of the total nitrogen of urine being transformed into 

 ammonia. The production of indole and the digestion of serum proteins varies 

 with different strains ; as a rule these two properties are negatively correlated. 

 The power to digest serum proteins is often lost during cultivation in the laboratory. 

 Catalase is formed, but the oxidase reaction described by Gordon and McLeod (1928) 

 is negative. 



Since the Proteus bacilli are found most constantly in decomposing animal matter, 

 they are generally regarded as putrefactive organisms. Rettger and Newell (1912-13) 

 dispute this. They define putrefaction as a " particular process of protein decomposition 

 which is brought about through the agency of bacteria with the evolution of foul-smelling 



