LABORATORY J FORK 31 r 



termine whether it is pure or not. For this purpose put a small 

 quantity of the culture from the package into a water blank, and, 

 by thorough agitation, distribute evenly through the water. From 

 this inoculate litmus gelatin tubes, some with one, some with two 

 and some with three loopfuls of the diluted culture. Pour into 

 petri dishes, incubate at 70°, and after three days examine to see 

 whether any bacteria can be found in the plate except lactic germs. 



42. Effect Upon Butter of Pasteurizing Cream. — -Divide 

 a lot of cream which is to be made into butter into two parts, pas- 

 teurize- one at a temperature of 155° for 15 minutes, leaving the 

 other without pasteurization. Add to each the same amount of 

 starter. Ripen in the usual way, churn and make into butter, and 

 compare the products, to see if any difference can be noted between 

 the butter from pasteurized and non-pasteurized cream. 



43. The Effect of Light Upon Butter.- — Place two lots of 

 butter, one in a bright light and one in the dark, and after several 

 days compare them as to .appearance, smell and taste. 



44. Ripening of Cream at Different Temperatures. — Divide 

 some cream into three lots. Place the usual amount of starter 

 in the cream, and ripen one lot at 50 , one at 65 ° and one at 85 °. 

 After proper ripeness has been reached (determined by acid test), 

 churn and compare the butter which is obtained, unsalted, to detect 

 any difference in flavor and aroma. 



45. Analysis of Bacteria in Cheese. — Determine the number 

 of bacteria in cheese exactly as above described for butter (see 

 experiment 38), making inoculation into litmus gelatin plates, and 

 determine the varieties of bacteria present. Make a series of plates 

 in this way from a freshly made cheese and another series from 

 some cheese ripened and ready for market. Compare the numbers 

 and kinds of bacteria. 



46: Effect of Different Species of Bacteria on Milk. — In- 

 oculate a series of sterile milk tubes with a large number of different 

 kinds of bacteria. It is well for this purpose to use all of the species 



