118 S. A. KOSER AND W. W. SKINNER 



in the destruction of the colon bacillus, irrespective of the effect 

 of carbon dioxide.^ 



Since it was found that Bad. coli is able to withstand carbona- 

 tion for an appreciable period, the next step was to investigate 

 the viabiUty under similar conditions of several of the patho- 

 genic members of the colon-tj^ihoid group. In these experi- 

 ments Bad. paratyphosum B and Bad. iyphosum were used. 

 It was at once apparent that both of these types are consider- 

 ably less resistant to the destructive effect of CO2 than is the 

 colon bacillus. Table 4 presents results which are character- 

 istic of a number of similar experiments. One point of particu- 

 lar interest is the persistence, at 1°C., of the last few surviving 

 organisms. These were too few in number to be estimated by 

 plating and their presence could be detected only by the culti- 

 vation of 10 cc. amounts in glucose broth. Additional experi- 

 ments with acid-containing beverages have shown that in these 

 the tjTJhoid bacillus is killed almost instantly. Thus Ln a car- 

 bonated lemon soda containing 0.156 per cent lactic acid, Bad. 

 iyphosum decreased in numbers from an initial inoculum of 

 27,400 per cubic centimeter to 10 per cubic centimeter within 

 one hour and after two hours its presence could not be detected. 



It should be emphasized that throughout all of the foregoing 

 experiments the water used for carbonation and for preparation 

 of the various beverages was an ordinary city supply of low 

 mineral content. Under certain conditions, as for example 

 in carbonated water of high mineral content, it is possible that 

 non-spore-forming organisms may remain alive for longer 

 periods than those herein reported. This possible influence of 

 certam inorganic salts upon the viability of microorganisms in a 

 carbonated enviromnent has not been studied in the present 

 investigation. 



' The usual methods of bacteriological analysis could not be applied when 

 larger quantities of the highly acid beverages were to be examined. It was 

 found that sufficient amounts of acid were carried over to the culture medium 

 to cause a distinct increase in the H-ion concentration, sufficient, indeed, to 

 effect a retardation or even complete inhibition of growth. By the use of larger 

 quantities of broth in flasks, instead of the usual amounts ordinarilj' contained 

 in test tubes, this difficulty was largely overcome. 



