21.2 



SCIENCE. 



[N. S. Vol. XXIII. No. 580. 



coagulative power of pathogenic, sewage 

 and fecal streptococci becomes equal to that 

 of milk streptococci by repeated passages 

 through milk. Streptococci from milk 

 form in long chains in lactose broth, and 

 the chains disappear upon inoculation in 

 litmus milk, and characteristic diplococci 

 and short chains of three to six members 

 appear instead. Artificial lactic acid fer- 

 mentations, produced by inoculation of 

 pure cultures of lactic acid bacteria of 

 either group or of cow feces in sterilized 

 milk, closely resemble the natural process. 

 Investigations lead to the following con- 

 clusions : 



1. Bacillus acidi lactici is a mj^th. The 

 ordinary bacteria producing lactic fer- 

 mentation are Bacilhis aerogenes var. lac- 

 ticus and Streptococcus lacticus. The pos- 

 sibility of B. coli participating in lactic 

 fermentation is not excliided. 



'2. Streptococcus lacticus (Kruse) agrees 

 in morphological, cultural and coagulative 

 properties with pathogenic, fecal and sew- 

 age streptococci. 



3. Souring of milk is caused by coopei'a- 

 tion of both groups of bacteria, and is par- 

 ticipated in by peptonizing bacteria always 

 present in milk. 



4. Gas is produced by B. aerogenes var. 

 lacticus, but as a rule is held in check and 

 ultimately stopped by the presence and 

 final ascendency of Streptococcus lacticus 

 (Kruse). 



5. Acid is produced during lactic fer- 

 mentation by both classes of organisms to 

 a marked degree. B. aerogenes var. lac- 

 ticus is more sensitive to the presence of 

 acid than Streptococcus lacticus (Kruse). 

 This results in the presence of B. aerogenes 

 in large numbers in initial stages of fer- 

 mentation, S. lacticus (Kruse) becoming 

 master tf the field in terminal stages. 



6. Lactic acid bacteria are of intestinal 

 origin and gain access to milk with par- 

 ticles of cow feces. 



7. Artificial lactic acid fermentation in 

 sterilized milk can be produced by inocula- 

 tion of pure cultures of bacteria of either 

 group or better by the two groups com- 

 bined. 



8. Since Streptococcus lacticus (Kruse) 

 is invariably present even in fresh milk 

 collected with good precautions, the sani- 

 tary significance of streptococci in market 

 milk will need further investigation. 



A Note on the Indol-producing Bacteria 

 in Milk (preliminary communication) : 

 S. C. Prescott, Massachusetts Institute 

 of Technology. 



The occurrence of indol-producing bac- 

 teria in milk suggests the possibility of 

 some connection between these organisms 

 and the intestinal diseases often so preva- 

 lent in children fed on raw milk, especially 

 that received in the larger cities, where the 

 milk may be forty-eight hours old before 

 it reaches the consumer. 



A large number of samples of fresh milk, 

 collected from about 175 different farms, 

 have been examined to determine if there 

 is any numerical relation between the indol- 

 producing bacteria and the total number 

 present in the milk. The samples were in 

 general about six hours old at the time of 

 the examination. The total numbers were 

 determined in the usual way by plating on 

 agar (reaction -|- 1) and incubating at 

 37.5° for twenty-four hours. Dilution of 

 1-10,000 was employed. Indol was de- 

 termined by inoculating 1/100 c.c. of milk 

 in a tube of peptone solution, incubating 

 three days at 37.5°, and then testing for 

 indol by adding a minute amount of sodium 

 nitrite and 1 c.c. of 1:1 sulphuric acid. 



In all 524 samples were examined, rang- 

 ing in total numbers from less than 5,000 

 to 121,000,000 bacteria per cubic centi- 

 meter. Of these but 38 samples exceeded 

 1,000^000 in total count; 132 samples, or 

 almost exaetl}^ 25 per cent., gave strong 



