ENZYMES. 41 
stirred in with the spatula. When the rennet thickens the milk 
sufficiently no more milk will run out and the operator notes the 
point on the scale to which the milk has run. The riper the milk 
the quicker it will thicken, with a corresponding lower reading 
on the seale. 
86. Importance of Tubes of a Uniform Bore in the Marschall 
Test. 
Originally a glass tube was used in the bottom of the basin, 
but as it proved impossible to get glass tubes of uniform bore, a 
metal tube was substituted and has been used in the test of late 
years, which has given good satisfaction. One can compare re- 
Fig. 21.—The Marschall Rennet Test. A, graduated cup; B, 1c. c. pi- 
pette; C, glass in which to dilute the rennet; D, spatula for stirring the milk. 
sults with the same test from one day to another, but confusion 
may result from comparing the results obtained with different 
tests if the bore of the tubes is not exactly alike. 
87. Errors to Be Avoided with Marschall Apparatus. 
1. As there is no thermometer included in the Marschall 
apparatus the operator is hkely to forget that temperature af- 
fects the rennet action. One should always temper the vessel 
in cold weather before using, and should carefully observe the 
temperature of the milk, both when starting the test and at the 
time of coagulation. A few degrees in temperature will modify 
the results very materially. 
2. One should exercise great care in running the milk into 
the milk in the vat. Where a large number of tests are made 
the rennet added may coagulate the milk. 
3. The results with two pieces of apparatus can not be com- 
pared until they have been used first in testing the same milk. 
