296 KEPORT OF OFFICE OF EXPERIMENT STATIONS. 



other stations. Aji orf^anisni causing bittor milk has been studied by 

 Conn." Bacteria causin<j ropy milk and cream have been described 

 by AVard ^ and Marshall.'^ 



The associative action of l)actoria in milk has been studied by 

 Marshall.'' who attaches considerable imi)()rtance to this subject in 

 practical dairying. As an illustration of the data secured by him, it 

 may be noted that mixed cultures of a lactic-acid bacillus and a 

 peptonizing species caused souring of milk 48 to 72 hours sooner than 

 pure cultures of the lactic-acid organism alone. 



Hunziker investigated the germicidal action of milk, concluding 

 that the " freshly draAvn milk of most cows contains varying ger- 

 micidal qualities." The germicidal action was found to be greatest 

 at 70° F., the average duration at this temi)erature being three to six 

 hours and the maximum twelve hours. At lower tem])eratures the 

 action was less marked, but of longer duration. Heating at 149° F. 

 for forty minutes destroyed the germicidal agent. No practical 

 means of utilizing this property of milk in improving milk supplies 

 was found. " So far as investigations up to the i:)resent time have 

 shown, the best means of improving the keeping quality of milk 

 Avithout the use of chemical i^reservatives seems to be scrupulous 

 cleanliness and low temperatures." 



The studies of Stocking '' concerning the so-called germicidal prop- 

 erty of milk have led to opposite conclusions. This author believes 

 that certain of the many species of bacteria gaining access to milk 

 as ordinarily produced find in the milk a medium unsuited for their 

 growth and hence disappear more or less rapidly. Other species, 

 including the lactic-acid group, find, on the contrary, conditions 

 favorable to their development and hence multiply more or less 

 rapidly. An increase or decrease in the bacterial content of the fresh 

 milk depends, according to this view, upon the nature of the organ- 

 isms present and the decrease often observed is, therefore, not prop- 

 erly to be attributed to a germicidal property, but is simply the 

 natural dropping out of the species, finding milk an unsuitable 

 medium in which to develop. 



The value of the thorough cleansing and ^sterilizing of dairy uten- 

 sils in lessening bacterial contamination, and hence improving the 

 quality of milk, has been often demonstrated in experiment station 

 work. An illustration may be cited from an article by Russell f 

 on the sources of bacterial infection. A covered milk pail was 



o Connecticut Storrs Sta. Rpt. 1890, p. 158. 



6 New York Cornell Sta. Buls. 165, 195. 



c Michigan Sta. Bui. 140. 



d Michigan Sta. Spec. Buls. 2.3, .33. 



e Connecticut Storrs Sta. Rpt. 1904, p. 89 ; Bui. 37. 



f Wiscousiu Sta. Kpt. 1894, p. 150. 



