STREPTOCOCCUS HEMOLYTICUS 205 



Chesney (1916) in a rather extensive investigation of the latent 

 period of bacteria noted variations in the toxicity of filtrates, 

 taken at intervals following the maximum period from plain 

 broth cultures. Inhibition appeared strongest at the time when 

 the culture had attained the summit of its growth and became 

 progressively less as the period of incubation increased. At the 

 point where the culture became sterile a minimum of inhibition was 

 shown. Filtrates taken early in the maximum period of growth 

 showed no inhibitory property while those taken near the end 

 of the same period proved to be somewhat toxic. According to 

 Chesney the inhibitory substances represent waste products of 

 the bacterial cells or unused portions of food molecules, and the 

 alteration of the cells occasioned by their exposure to these 

 toxic materials is concerned with that structure or function 

 which is essential to metabolism and hence to growth. It must 

 be emphasized that in Chesney's experiments plain broth cul- 

 tures were studied and that consequently the factor of acidity 

 was absent. In fact no determinations of hydrogen-ion concen- 

 tration were carried out. 



It is a well recognized fact that plain broth cultures of the 

 streptococcus remain viable throughout much longer periods 

 than do glucose-broth cultures of the organism. This would 

 tend to substantiate the conclusion drawn from experiment XII 

 that acidity is the chief single factor causing inhibition and death 

 of the streptococcus. Natvig (1909) in an investigation of acid 

 production by the streptococcus arrived at the same conclusion. 



Refrigeration of streptococcus cultures is known to be one of 

 the best means of maintaining the viability of the organisms and 

 it has been observed in this laboratory that such a procedure is 

 especially useful in preserving the pleuritic exudates employed 

 as a source of culture material in the present investigation. It 

 would be expected that the decrease in temperature occasioned 

 in transferring a culture from the incubator to the ice chest 

 would reduce the rates of metabolism and growth to a low level. 

 As a consequence the toxic products of bacterial metabolism 

 would increase in the medium at a much slower rate than if the 

 culture were incubated. Obviously this condition would tend to 

 preserve the viability of a culture for long periods. 



