172 MODERN METHODS OF TESTING MILK 



bottle and allowing it to run back into the bottle. Mix 

 well by shaking. Then place the milk to be tested 

 in the test-cup, setting it in a level position and allow- 

 ing the milk to run out at the bottom. Taking the bot- 

 tle of diluted rennet in one hand and the spatula in 

 the other, watch the level of the milk in the cup. The 

 moment the upper surface of the milk drops to the 

 zero mark,,; pour the diluted rennet into the milk and 

 stir well. Then leave it alone. When the milk coagu- 

 lates, it stops running through the metal tube. From 

 the graduated scale, read the number of spaces un- 

 covered on the inside of the cup, showing how many 

 divisions of milk have run out. The more slowly the 

 milk coagulates, the larger the amount that runs out; 

 the more quickly the milk coagulates, the smaller the 

 amount that runs out and the fewer spaces there are 

 uncovered. When about 2^2 spaces are uncovered, 

 the milk is ready for addition of rennet. The tempera- 

 ture must be watched, being tested at the start and 

 finish, especially in a cold room. 



In the Marschall test, as originally devised, there 

 were some objectionable features. Formerly, glass 

 tubing was used in the bottom of the cup and it was 

 found that the size of the bore of tubing unavoidably 

 varied in different cups. This made it impossible to 

 compare the results of one cup with those of another, 

 unless they were proved by actual testing to be alike. 

 This difficulty has been overcome by dispensing with 

 the use of glass tubing and substituting in its place 

 aluminum tubing with the hole drilled to uniform ex- 

 actness. One difficulty connected with the use of the 

 Marschall test is that a little speck of dirt quickly 



