Reducing Properties of Milk. 185 



bacterial cell, which do not pass into the filtered fluid (Schar- 

 dinger, Spina, Cahen). 



From the above mentioned facts it is evident that milk which 

 contains numerous bacteria has a strong reducing property. 

 Through the works of Smidt, Miiller, and Schardinger it has been 

 proved that as a rule the richer the milk is in bacteria the earlier 

 the reduction of the aqueous methylene blue solution at 37 deg. 

 will occur. Milk drawn under sterile conditions fails to reduce the 

 methylene blue solution even after days (Rullmann). Miiller 

 proved that freshly drawn and cleanly handled market milk re- 

 quires 10, 12 or more hours for reduction (mixing 10 parts to 1 part 

 of methylene blue solution), whereas fresh market milk during 

 cold weather requires 6 to 9, and in warm weather only 1 to 2 hours 

 for the decolorization. At the stage when bacteria begin to multi- 

 ply, which is at the end of the incubation period, the time required 

 for reduction amounts to from 1 to 2 hours. If sour milk or cow 

 manure was added to fresh milk the time of reduction was 

 hastened. 



He therefore proved that all factors which favorably influence 

 bacterial growth hasten the reduction. 



In the author's first investigation he found that 10 c. c. of milk with about 44,000 

 bacteria per c. c. failed to reduce one c. c. of methylene blue solution in six hours. 



With about 200,000 bacteria reduction took place in 4 to 6 hrs. 



With about 500,000 bacteria reduction took place in 3.5 hrs. 



With about 1,600,000 bacteria reduction took place in 2 hrs. 



With about 6,000,000 bacteria reduction took place in 70 min. 



With about 350,000,000 bacteria reduction took place in 50 min. 



With about 800,000,000 bacteria reduction took place in 15 min. 



Similar results were obtained by Jensen as follows: 



With about 264,000,000 bacteria reduction took place in 1 min. 



With about 80,000,000 bacteria reduction took place in 3 to 5 min. 



With about 50,000,000 bacteria reduction took place in 10 min. 



With about 7,000,000 to 11,000,000 bacteria reduction took place in 40 to 60 min. 



With about 3,000,000 bacteria reduction took place in 2% hrs. 



With about 1,600,000 bacteria reduction took place in 7% hrs. 



With about 1,000,000 bacteria reduction took place in 6% hrs. 



With about 126,000 bacteria reduction took place in 9^ hrs. 



Since the degree of acidity increases with the growth of bac- 

 teria there exists a certain connection between the degree of acidity 

 of the milk and the rapidity of reduction, and since the degree of 

 acidity increases rapidly after incubation, a rapid reduction would 

 be expected to follow a rapid increase in the degree of acidity. 



This is also proved by Jensen 's experiments. Milk which reduced in one minute 

 had after 12 hours, at 25 deg. C., a degree of acidity of 36. 

 Milk which reduced in 



5 min. after 12 hrs. at 25 deg. had an acidity of 19 



8 min. after 12 hrs. at 25 deg. had an acidity of 20 



6 min. after 12 hrs. at 25 deg. had an acidity of 35 



10 min. after 12 hrs. at 25 deg. had an acidity of 22 



8 min. after 12 hrs. at 25 deg. had an acidity of 18 



7 min. after 12 hrs. at 25 deg. had an acidity of 28 



1 hr. after 12 hrs. at 25 deg. had an acidity of 15 



y 2 hr. after 12 hrs. at 25 deg. had an acidity of 25.5 



1% hr. after 12 hrs. at 25 deg. had an acidity of 11.5 



