Rural School Leaflet. 729 



much more slowly if kept cold. For this reason the bacteria in the warm 

 milk will grow faster and change the milk sugar into acid more rapidly, 

 causing the milk to sour and curdle before it does in the jars which have 

 been kept at the cooler temperatures. 



Note. — It will be well to start this experiment as early in the morn- 

 ing as convenient, and maintain the different temperatures during the 

 day, making an occasional observation to determine when the milk be- 

 gins to sour. 



It will be well to start with milk which is a few hours old, so that 

 which was kept at the \yarmest temperatures will curdle before night. 

 Probablv the bottle kept in ice-water, and possibly the one at 50^ will 

 not curdle before the next day. 



It can be explained to the pupils that the souring and curdling of 

 the milk is the direct result of the growth of the bacteria, which are 

 too small to be seen. 



Fig. 52. — Method of keeping samples at different temperatures. 



THE BABCOCK TEST 



Alany encouraging letters have been received from teachers who have 

 made experiments with the apparatus sent out for the Babcock test. We 

 find that the teachers are making the most of this opportunity for giving 

 some definite instruction in agriculture. Following is a letter received 

 from one of the teachers who feels that the work has been worth the 

 while. R. F. D. 2, Castorland, N. Y., 



Dec. 18, 1907. 



Dear Miss McCloskey: 



We have used the tester in our school, and with very good success. 



The first day I explained the different utensils used ; another, the 

 scale on the bottles and gave exercises in reading different tests ; the next, 

 the children practiced reading with oil and water in the bottle ; another, 

 the use of pipette and acid measure. When they had become proficient 

 in using the tester with water, we made a real test, following directions 

 accurately. One sample tested six per cent. ; another three and two- 



