THE DEPORTMENT OF RENNET. 45 
cylinder. Next make a rennet test of the milk. It curdles the 
milk, showing that rennet is an enzyme. 
95- Thermal Destruction Point. 
At about 104° or 105° F. rennet in weak solutions is de- 
stroyed. 
Experiment (a). Make a rennet test of a sample of milk 
and note the number of seconds required. Next heat the rennet 
solution to 100° for ten minutes and try a test with it on the 
same milk. Try heating it to 105°, 110°, 115° and 120° for five 
minutes and make tests after each heating. Do not forget to 
record the results in your notebook. 
Experiment (b). Note the length of time required to co- 
agulate 160 ¢. ce. of milk at 86° F. with 5 ec. ¢. of strong com- 
mercial rennet extract. Next heat a portion of this strong ren- 
net to 150° F. for five minutes and note the length of time re- 
quired for coagulating 160 ¢. ¢. of milk at 86° F. with 5. «. 
of the extract. 
96. Effect of Strength of Rennet Solution. 
For a long time it was supposed that as the strength of the 
rennet solution was increased, the length of time required for 
coagulation was inversely shortened. This, however, is not true. 
Experiment (a). Make a rennet test of a sample of milk. 
1. Make up a new solution of rennet, measuring twe 5 e¢. ¢. 
pipettefuls of rennet in the 50 ¢. c. flask. This makes the ren- 
net solution twice as strong as the solution commonly used. 
Note the time required for coagulation with this solution. 
2. Make up a solution with three pipettefuls, or 15 c. c. of 
rennet in the 50 ¢. c. and make a test. 
3. Make up a solution with four pipettefuls, or 20 ¢. ¢. in 
the 50 ec. c. What are the results? 
4, Make up a solution with 25 ¢. c. of strong rennet diluted 
to 50 ¢. ¢ It is suggested that the student secure a piece of 
cross-section paper and chart out the results obtained. If the 
rate of coagulation be diminished inversely in proportion to the 
increase in strength the results of these tests would, when re- 
corded, make a straight line across the chart, whereas they really 
make a curved line. 
