GROWTH REQUIREMENTS 



533 



but the meningococcus will not do so ; the addition, however, of a small quantity 

 of blood or serum is sufficient to enable growth to occur. The most fastidious 

 is the gonococcus ; to cultivate this organism a great variety of media have been 

 devised, the majority depending on the addition of some natural protein such as 

 blood, serum, ascitic fluid, or hydrocele fluid to a basis of nutrient agar. The 

 meningococcus and the gonococcus are not always easy to maintain in culture ; 

 even though transplants are made every 2 or 3 days, the organisms not infrequently 

 die out, and the strains are lost. 



All the members of the group are aerobic ; little or no growth occurs under 

 strictly anaerobic conditions. Growth of the gonococcus is favoured by the 

 addition of cystine or other source of — SH bodies (McLeod et al. 1927, Boor 1942). 

 Many workers have stated that the meningococcus and the gonococcus grow best 

 under a lowered oxygen pressure, and that their growth is improved by 10 per cent. 



I % 



Fig. 101.— Neisseria gonorrhoece. 



From a blood agar slope culture, 24 hours, 

 37° C. (X 1000). 



Fig. 108. — Neisseria pharyngis. 



From a blood agar slope culture, 24 hours, 

 37° C. (X 1000). 



CO2 (Wherry and Oliver 1916, Chapin 1918, Kohman 1919, Ruediger 1919, Rock- 

 well and McKhann 1921) ; but numerous other workers have failed to substantiate 

 this (Cook and Stafford 1921, Erickson and Albert 1922, Torrey and Buckell 1922a). 



When making experiments on the effect of altering the gaseous constitution of the 

 atmosphere, it is very difficult to control all the factors concerned ; the technique used 

 may, for instance, change the moisture content of the atmosphere and the rate of evapora- 

 tion from the medium. The presence of 10 per cent. CO2 alters the H-ion concentration, 

 and will interfere with the change in the reaction of the medium that normally occurs 

 diu-ing growth ; thus CO2 may be beneficial if the medium has been made too alkaUne, 

 and it may by its buffering action prevent the accumulation of acid. The failure to 

 standardize these secondary factors is probably sufficient to explain the diverse results 

 obtained by different workers. 



The work of McLeod and his colleagues (1934), however, does suggest that 

 growth is improved by the addition of 10 per cent. CO2, particularly that of freshly 

 isolated strains. Glucose and glycerine have little or no beneficial effect ; peptone 

 iu a 1-3 per cent, concentration seems to be favourable. The optimum H-ion 

 concentration for growth is about pH 7-4-7-6 ; the limits within which growth 



