96 EXPERIMENTAL DAIRY BACTERIOLOGY 



1. A definite quantity of the butter may be weighed, as 

 for example, 1 gram. If the butter to be sampled is in the 

 form of a pound print, a piece should be cut from one end 

 with a sterile knife, and the sample taken from various por- 

 tions of the freshly exposed surface. If the butter is in a tub 

 or jar, the sample should be taken with a sterile trier, the 

 plug thus taken split with a knife, and portions taken from 

 various parts of the plug. The butter can be weighed by plac- 

 ing on the pan of the balance a circular piece (9 cm.) of sterile 

 filter paper. Filter papers of this kind should be sterilized in 

 a Petri dish and kept in stock. On the larger filter place a 

 7 cm. filter paper, on which the butter is to be placed. The 

 contamination from the air during the weighing process will 

 be of no appreciable importance. The smaller filter with 

 the butter should be transferred by means of sterile forceps 

 to a definite volume of sterile water, which is then heated 

 from 40 to 45 C. in order to melt the butter and to distrib- 

 ute the bacteria uniformly. The sample for further dilution 

 should be removed while the contents of the flask are well 

 emulsified. 



2. Instead of weighing the butter it may be melted at 

 40-45 C. and 1 cc. removed with a warm pipette and trans- 

 ferred to warm sterile water. The pipette should be freed from 

 the adherent fat by filling it with the dilution water a number 

 of times. Further steps in the preparation of the plate cul- 

 tures and in their study are carried out as described in the 

 case of the examination of milk. 



Relation of age of butter to bacterial content. Butter is 

 made up mainly of butter fat, water saturated with salt, and 

 small quantities of the other ingredients of milk. It contains 

 but little proteid matter, and is therefore not well suited for 

 bacterial growth, The difference between the germ content 



