20 MASS. EXPERIMENT STATION BULLETIN 369 



stances which are absorbed into the body and there cause some poisoning effect. 

 Indol is one of these substances, and it is produced by the colon bacillus which is 

 common in the human intestine. It is known that when plenty of sugar is avail- 

 able for the bacteria, little or no indol is produced. This is especially true when 

 the sugar is dextrose, the form to which all starch and sugar in food is digested 

 in the intestine. Studies were made in culture media on factors that might 

 influence indol production by the colon bacillus. Results: 1, All common sugars 

 (dextrose, lactose, maltose, sucrose), starch, and dextrine checked indol produc- 

 tion. 2, Control of intestinal acidity by calcium carbonate or dipotassium phos- 

 phate did not check indol production. 3, Acidity did not check indol production 

 unless the acid was concentrated enough to interfere with growth of bacteria. 

 4, Bile and bile salts did not interfere with production of indol. 5, When Aero- 

 bacter aerogenes was grown with Escherichia coli in a medium containing one-half 

 of one percent of dextrose, the combined cultures appeared to use the dextrose 

 so that the production of indol by the colon bacillus proceeded as if no dextrose 

 had been present. The study on indol production is being continued. 



The Influence of Bacteria on the Oxidation of Ascorbic Acid. (W. B. Esselen. 

 Jr., and James E. Fuller.) This study has been completed and published in two 

 journal articles: Journal of Bacteriology 37:501-521, 1939 (Contribution No. 319); 

 and Food Research 4:329-334, 1939 (Contribution No. 326). 



Relationship of Onion Juice to Bacterial Growth. (James E. Fuller and Ernest 

 R. Higgins.) For many years the belief has persisted that onions and garlic have 

 the power to prevent bacterial growth. Some success has been reported in the 

 use of garlic to prevent spoilage of pickles, and even from the use of garlic in the 

 treatment of tuberculosis. More recently papers have been published reporting 

 the ability of onion and garlic vapors to prevent bacteiial growth. The present 

 study was made to determine the value, if any, of onions to control bacterial 

 growth in pickles and relishes. The effect of onion juice in culture media was 

 studied with several species of bacteria, with results as follows: (1) Aerobacter 

 aerogenes was entirely resistant to the juice, and (2) Escherichia coli was nearly so. 

 (3) Salmonella schottniulleri, (4) Pseudomonas pyocyanea, and (5) Staphylococcus 

 aureus did not grow in concentrations much above 50 percent of juice, but the 

 bacteria were not killed. (6) Proteus vulgaris and (7) bacteria of the Bacillus 

 subtilis group grew only in low concentrations of juice, and in the more con- 

 centrated juice the bacteria were killed. The first four species are human in- 

 testinal bacteria; the fifth is from the skin, and can cause food poisoning; the sixth 

 is common in putrefying substances; the seventh is from dust and soil. Live steam 

 weakened the bactei ia-controUing property of the juice as compared with sterili- 

 zation by filtration, and steam-pressure sterilization practically destroyed the 

 property. The juice still could hinder bacterial growth even though experiments 

 showed that the vapors were no longer potent. 



Studies of Cocci from Swimming-Pool Water. (James E. Fuller and R. H. 

 Guiberson.) Cocci are significant in swimming-pool water because those from the 

 nose and throat can cause infections in pool users, while ihose from the intestine 

 are less dangerous and probably entirely harmless. When cocci are isolated from 

 swimming-pool water, it is important that they be identified as intestinal or non- 

 intestinal. As a beginning of a study of identification methods, a group of cocci 

 identified as intestinal by commonly used methods were studied further. It was 

 found that a pH value of 10.7 and 15 percent common salt in the medium, r es 

 pectively, in place of pH 9.6 and 6.5 percent salt commonly used, made it possible 

 to separate the cocci studied into two fairly distinct groups. The study is being 

 continued. 



