58 EXPERIMENTAL DAIRY BACTERIOLOGY 



Exercise. Each student will make a quantitative examination of 

 fresh manure and also of dried manure removed from the flanks 

 of cows. 



A piece of sterile filter paper 4 inches square is placed on the scale 

 pan, and on this a smaller piece. One gram of manure is weighed out 

 on the sterile filter paper ; the upper paper and manure are trans- 

 ferred to a flask of sterile water (500 cc.). Make as even a suspen- 

 sion as possible. The dilutions should be very large, especially in 

 case of the fresh manure, 1/10,000, 1/100,000, and 1/1,000,000 

 grams, for example. 



Plain agar medium should be used and the plates incubated for 

 forty-eight hours at 37 C., or at 20 C. for four to five days. 



Express the results as the number per gram of sample examined. 



Contamination from hair. Hairs removed from the flanks 

 and udders of even the cleanest animal bear more or less dust 

 and bacteria. The extent of this contamination can be meas- 

 ured by removing, with a pair of scissors, some of the long 

 hairs from the udders and flanks and placing them in sterile 

 Petri dishes for transportation to the laboratory. Lactose- 

 gelatin plates are prepared as previously. When the plates 

 are well solidified three or four hairs are placed on the sur- 

 face of the medium by means of a pair of forceps or the 

 platinum loop. The hair should be pressed down so as to 

 be thoroughly in contact with the medium. A separate cul- 

 ture dish should be used for the hairs from different animals. 

 The results should be expressed as the average number of 

 bacteria per linear inch on the hairs removed from the vari- 

 ous animals. 



Exercise. Each student will collect several individual hairs from 

 four animals showing varying degrees of cleanliness, and determine 

 the number of organisms on the same, noting the relative number 

 of molds, liquefying and nonliquefying bacteria. 



Contamination from interior of udder. Bacteria may gain 

 entrance to the interior of the udder and establish themselves 





