BACTERIAL CONTENT OF MILK IN THE UDDER 269 



By this method obtain from the same teat: 



a. One sample of the fore milk, 



b. One sample of the middle milk; 



c. One sample of the strippings; 



Note. For investigational purposes it may be better to employ 

 a sterile milking tube adjusted to a sterile flask. This may easily be 

 prepared. This method, however, is not recommended for student 

 work. 



3. Secure one sample from the pail, gathered from the 

 same cow at the same milking. 



4. Plate each sample on litmus lactose agar, using the 

 following dilutions and amounts: 



1 c.c. of 2a diluted 1 : 100 for the plate. 

 1 c.c. of 26 diluted 1 : 10 for the plate. 

 1 c.c. of 2c diluted 1 : 10 for the plate. 

 1 c.c. of 3 diluted 1 : 100 for the plate. 



5. Place the plates at a temperature of 21 C. for seven 

 days. 



6. Count the number of colonies in each plate and 

 record the average number in 1 c.c. of milk in each case. 

 Explain any variation in counts. 



7. Compare the colonies of plates 2a, 26, and 2c with 

 3. What types predominate? 



8. Estimate, so far as possible, the number of colonies 

 of each type, and compare the relative numbers of each 

 species in the different plates. 



9. Isolate the species in milk tubes to study their action 

 upon milk. To what group of microorganisms found in 

 milk does each of the species isolated belong? How do you 

 account for the presence of these particular species? 



10. In which sample would you expect to find the greatest 

 number of microorganisms? Why? 



Why should all samples be taken from the same quarter 

 of the udder? 



How do bacteria ordinarily gain entrance to the udder? 



