7O A DAIRY LABORATORY GUIDE 



EXERCISE XIII 



BABCOCK TEST, MICROSCOPIC APPEAR- 

 ANCE OF MILK, USE OF RENNET 



1. Test the composite sample preserved at the last 



exercise. 



2. Examine under the high-power microscope 



cream, whole milk and skimmed milk. Make 

 a drawing of each field. Describe fully the 

 difference in the appearance of the fat 

 globules in each of the three fields. 



3. Heat 18 grams of skimmed milk to about 100 



F. and add four drops of rennet ; shake thor- 

 oughly and let stand. Note the length of 

 time it takes the milk to curdle. 



4. To one-half a teacup of water add six drops of 



sulphuric acid. Add three drops of this solu- 

 tion to 18 grams of milk. Heat to about 

 100 F. and add four drops of rennet and 

 note the time it takes for milk to coagulate. 

 Compare length of time with that required 

 in No. 3. 



5. To about 20 grams of skimmed milk add six 



drops of sulphuric acid and shake thoroughly. 

 Note time it takes the milk to coagulate and 

 compare the coagulum with that obtained 

 when rennet is used. 



6. Measure out two 25 cc. samples of skimmed 



milk. Warm to 80 F. To one sample add 

 five drops of rennet ; to the other add five 

 drops of sulphuric acid. Note and compare 

 the length of time it takes each to coagulate. 



