EXERCISE XXVIII. 



A STUDY OP BACTERIA IN MILK. 



It is desirable to understand somewhat clearly the 

 bacterial contents of milk and to know something of the 

 physiological properties of these bacteria. For this reason 

 it is desirable to study though but briefly the bacteria in 

 ordinary market milk. 



References. — Dairy Bacteriology, Russell ; also one 

 by Conn, and one by Grotenfelt. Hunziker, Germicidal 

 action in cows milk. Bulletin No. 197, Cornell Univ. Exp. 

 Station. Ward, The invasion of the udder by bacteria. 

 Bulletin 178, Ibid. Park, Bacterial contamination of the 

 milk of our cities. The N. Y. Univ. Bulletin of the Med. 

 Science, Vol. i. Moore, Bacteria in milk. Report of the 

 Com. of Agriculture of N. Y., 1902. 



^Vork for this Exercise. — Examine the plate cultures 

 made from milk. Describe the different kinds of colonies 

 and state approximately the number of each. Examine 

 microscopically the bacteria in one of each kind of colonies 

 and determine its genus. 



Inoculate a tube of milk and one of gelatin from each 

 of three different kinds of colonies, stating the genus of the 

 bacteria in each. 



Describe the cultures of B subtilis. 



Inoculate groups A and B of media from a culture of 

 B. prodigiosus furnished. 



Make for examination at the next exercises a series of 

 three gelatin plates from a sample of water furnished, (un- 

 filtered creek or well water) using the quantity for each 

 culture designated by the instructor. 



