352 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 9 



They were thus enabled to differentiate between those organisms 

 that may be pathogenic to man and those that are not. 



Fennell and Fisher (II, '19), working with cultures of pneu- 

 mococcus and meningococcus, were often unable to obtain suit- 

 able growth although the media utilized had apparently the same 

 composition, was made in the same way, and the titration by 

 the Fuller method was always adjusted to the same point, -j-0.2 

 (0.2 per cent). Using the hydrogen-ion concentration in their 

 titration they obtained profuse and consistent growth. They 

 found that pneumococcus has a very narrow range for optimum 

 reaction, P H 7.8 to P H 8.0, which they considered as equal to +3.0 

 to +3.5 (3-3.5 per cent), "a total acidity far beyond anything 

 previously suggested for the growth of pneumococcus." Norton 

 (II, '19) obtained similar results. 



Not only has the hydrogen-ion concentration been used suc- 

 cessfully for distinguishing between closely related organisms, 



but its use in the study of various phases in metabolism has 

 yielded valuable results. Its relationship to the growth of pneu- 

 mococcus and meningococcus has just been pointed out. In ad- 

 dition it may be noted that Cole and Lloyd (II, '17) showed that 

 among other factors, a suitable hydrogen-ion concentration is 

 important for the cultivation of gonococcus. There are now nu- 

 merous records like these which show the relationship of growth 

 and development of many different micro-organisms to hydrogen- 

 ion concentration. Concerning its relationship to definite physi- 

 ological reactions there are also numerous records; for example, 

 Bronfenbrenner and Schlesinger (II, '19) pointed out that the 

 amount of acid and gas produced by bacteria depended on various 

 factors, including the amount of carbohydrate, the amount of 

 peptone, the amount of buffer, and on the hydrogen-ion concen- 

 tration; Bigelow and Esty (II, '20) showed that a slight change in 

 the hydrogen-ion concentration greatly affected the thermal 

 death point, and Chambers (II, '20) gave accurate counts of the 

 number of bacteria developed at different levels of hydrogen-ion 

 concentration. Studies on non-pathogenic bacteria and fungi, 

 as well as on higher plants, have shown similar relationships to 

 hydrogen-ion concentration. The work of Allen (II, '19) on 

 Azotobactcr, Gillespie and Hurst (II, '18) on Actinomyces scab- 

 ies, Rose (II, '19) on Nummularia discrcta, and Duggar (II, '20) 

 on nutrient solutions for higher plants, to mention but a few, has 



