TESTING THE SANITARY CONDITIONS OF MILK 159 



blue; this does not combine with casein and is easily 

 absorbed by living cells. A solution of this is pre- 

 pared by putting a few grams of a solution of methyl- 

 ene-blue (using the zinc chloride double salt) into 

 20 cc. of alcohol and letting it stand at room tempera- 

 ture for 2 hours. Of this saturated solution take 5 cc. 

 and mix it with 195 cc. of distilled water. 



To perform the Barthel form of the test, add I cc. of 

 the dilute methylene-blue solution to 20 cc. of milk and 

 put the mixture in a warm place (113 to 122 F.). 

 If the blue color disappears within an hour, the milk is 

 to be regarded as very bad from a sanitary point of 

 view and wholly unfit for the use of infants. If the 

 color disappears within 3 hours, the milk is classed as 

 of second quality ; milk which remains wholly un- 

 changed after the lapse of 3 hours is to be regarded as 

 good. 



Another simple way of performing the test is to 

 mix 25 cc. of milk and 6 drops of a solution of pure 

 methylene-blue ( 1 14000) in a cylinder. After shaking, 

 the cylinder is stoppered with a cotton plug and put in 

 a water-bath at 104 F. If the color disappears in less 

 than 15 minutes, the milk is condemned. 



This test is used as a rough measure of the num- 

 ber of bacteria in milk, since the decoloration or reduc- 

 tion of methylene-blue in milk appears to be due whol- 

 ly to the activity of micro-organisms. The decolor- 

 ation takes place in 5 minutes or less when the number 

 of bacteria exceeds 10 millions per cubic centimeter. 



Jensen's "reduction-fermentation" test is a modifica- 

 tion of the Barthel method, using only 0.5 cc. of methyl- 

 ene-blue solution (instead of i cc.) and heating at 



