3OO PRACTICAL DAIRY P.ACTKKH >L< x ,Y 



the actual number in manure it is necessary to weigh the original 

 bit -of manure and make subsequent calculations. 



No. 43. Isolation of B. Coli. Repeat No. 42, using litmus 

 agar. If any strong acid surface colonies appear, choose one 

 that shows a gas bubble if possible ; isolate, inoculate on an agar 

 slant, and purify as usual. From the purified culture inoculate 

 a glucose fermentation tube. If gas appears, examine the cul- 

 ture and determine whether the bacterium is a short motile rod. 

 If so, the species is probably B. coli; if it is not motile, it is 

 probably B. aerogenes. Compare with page 34. 



No. 44. Bacteria on Hair. Melt a tube of agar and one of 

 gelatin, and pour into Petri dishes. After they have hardened 

 place upon the surface of each one or two hairs from the flank 

 of a cow. Two or three days later examine, and note the 

 numerous bacterial colonies growing along the course of the 

 hairs. 



*No. 45. Fore Milk. Draw the first 3 sets of milk from one 

 teat of a cow into a sterile test tube. Now milk the cow about 

 one-half dry and draw 6 more jets in a second sterile tube. 

 Remove to laboratory and plate at once in plain gelatin, diluting 

 10 times. Compare the numbers and kinds of colonies in the 

 two sets of plates. 



No. 46. Bacteria on the Hands. Wash the hands, thoroughly 

 in 200 c.c of sterile water. Place i c.c. of this water in a tube 

 of melted agar. Count the colonies and calculate the number 

 of bacteria removed from the hands by the washing. 

 , No. 47. Estimation of Dirt in Milk. 1 Procure some milk from 

 a clean and carefully kept dairy and also some from a dairy 

 where the milking is done in a careless, slovenly fashion. De- 

 termine the amount of dirt in the milk in each case, as follows : 



a. First method. Place a quart or a liter of each sample of 

 milk in a tall glass cylinder, and allow it to stand for several 



1 This experiment is impossible without a chemist's balance and apparatus 

 for drying, such as used in quantitative chemistry and analysis. 



