STBEPTOCOCCUS HEMOLYTICUS 



Reaction of differential media 



201 



V. THE RELATION OF HYDROGEN-ION CONCENTRATION TO INHIBI- 

 TION AND DEATH OF STREPTOCOCCUS HEMOLYTICUS 



It has long been noted that the growth of a microorganism be- 

 yond a certain point exhibits symptoms of inhibition, manifest 

 first in a decreasing growth rate, second by complete cessation 

 of growth, third by a definite decrease in numbers, and finally 

 by death, at which point the culture becomes entirely sterile. 

 Inhibition, representing as it does an almost universal bacterio- 

 logical phenomenon, ensues from the toxic action of the products 

 of its own metabolism upon the organism itself. Through the 

 continuous accumulation of these waste products in the encom- 

 passing medium and through the inabiUty of the organism to 

 escape their contact inhibition becomes more and more pro- 

 nounced and eventually death supervenes. If the metabolic 

 products are largely of acid nature these substances will exert a 

 harmful effect and if in greater concentrations, a fatal influence. 

 This fact has been well illustrated in the curves of acid formation 

 previously discussed. 



Recognizing this principle, Kitasato (1888) in 1888 added 

 various acids to neutral media and then determined the mini- 

 mum dose required to kill Bad. typhosum and V. cholerae, and 

 the maximum dose which would still permit their growth. As 

 the results of these experiments were expressed only in terms of 

 percentage concentration they have for us now only historical 

 interest. 



